[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
** Changed in: linux (Ubuntu) Status: In Progress => Fix Released -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: Fix Released Status in linux-lowlatency package in Ubuntu: Fix Released Status in linux source package in Focal: Won't Fix Status in linux-lowlatency source package in Focal: Won't Fix Status in linux source package in Groovy: Won't Fix Status in linux-lowlatency source package in Groovy: Won't Fix Status in linux source package in Hirsute: Won't Fix Status in linux-lowlatency source package in Hirsute: Won't Fix Status in linux source package in Jammy: Won't Fix Status in linux-lowlatency source package in Jammy: Won't Fix Status in linux source package in Lunar: Won't Fix Status in linux-lowlatency source package in Lunar: Won't Fix Status in linux source package in Mantic: Won't Fix Status in linux-lowlatency source package in Mantic: Fix Released Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
** Description changed: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. + The results didn't show any performance regression: + + https://kernel.ubuntu.com/~mhcerri/lp1919154/ + [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: In Progress Status in linux source package in Hirsute: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
https://lists.ubuntu.com/archives/kernel-team/2021-April/118905.html -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: In Progress Status in linux source package in Hirsute: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Results: https://kernel.ubuntu.com/~mhcerri/lp1919154/ ** Changed in: linux (Ubuntu Groovy) Status: New => In Progress ** Changed in: linux (Ubuntu Focal) Status: New => In Progress -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: In Progress Status in linux source package in Hirsute: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
** Also affects: linux (Ubuntu Jammy) Importance: Undecided Status: New ** Also affects: linux (Ubuntu Mantic) Importance: Undecided Assignee: Marcelo Cerri (mhcerri) Status: In Progress ** Also affects: linux (Ubuntu Lunar) Importance: Undecided Status: New ** Changed in: linux (Ubuntu Jammy) Status: New => In Progress ** Changed in: linux (Ubuntu Lunar) Status: New => In Progress ** Changed in: linux (Ubuntu Jammy) Assignee: (unassigned) => gerald.yang (gerald-yang-tw) ** Changed in: linux (Ubuntu Lunar) Assignee: (unassigned) => gerald.yang (gerald-yang-tw) ** Changed in: linux (Ubuntu Mantic) Assignee: Marcelo Cerri (mhcerri) => gerald.yang (gerald-yang-tw) -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Since we have some customers need NO_HZ_FULL, I'd like to provide some updates and progress: I've borrowed some machines including intel, AMD EPYC, arm64 servers and now running some tests on a test kernel with 1. CONFIG_NO_HZ_FULL=y 2. not enable nohz_full in kernel cmdline to evaluate if there is any performance impact Old kernel seems to have some issues with NO_HZ_FULL built-in but not enable So I will focus on kernel >= 5.15 For 5.15 test PPA (built with CONFIG_NO_HZ_FULL=y): https://launchpad.net/~gerald-yang-tw/+archive/ubuntu/no-hz-full for other versions 5.19 and 6.2, I will create more test PPAs for them and keep updating the test status here Thanks, Gerald -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
jammy hwe kernel (6.2) with NO_HZ_FULL: https://launchpad.net/~gerald-yang-tw/+archive/ubuntu/no-hz-full-6.2 -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Test program from Jay ** Attachment added: "syscall-time.c" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+attachment/5710594/+files/syscall-time.c -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
The attached test code is borrowed from Jay, it measures the average time for running getpid() 1 times to see if NO_HZ_FULL will cause any performance degradation for context switch when it’s built into kernel There are 4 test scopes: 1. Without NO_HZ_FULL built-in the default value of NO_HZ is NO_HZ_IDLE in ubuntu kernel 2. With NO_HZ_FULL built-in, but not activate it in kernel cmdline 3. With NO_HZ_FULL built-in, and activate nohz_full on some CPUs (also isolcpu and rcu_nocbs) in kernel cmdline 4. With NO_HZ_FULL built-in, and activate nohz_full on some CPUs, but run test program on a non-activate nohz_full CPU For the first 3 test scopes above also contain two test cases 1. Not pin the test program 2. Pin the test program to a specific CPU, in my test, it’s pinned to CPU 4 as below taskset --cpu-list 4 ./test For the forth test scope, only pin the test program to a specific CPU which is not in nohz_full -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Results on Intel machine Hardware configs: Dell PowerEdge R730xd Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz 40 CPUs 188G RAM, numa nodes: 2 Software configs: OS: ubuntu 20.04 Official kernel: 5.15 hwe (5.15.0-86.96~20.04.1) Test kernel: 5.15 hwe (5.15.0-86.96~20.04.1+test20231013b0) https://launchpad.net/~gerald-yang-tw/+archive/ubuntu/focal-no-hz-full Test case 1, without NO_HZ_FULL built-in (default ubuntu kernel config): Run test program 4 times without taskset tail -n 2 log/notaskset.* ==> log/notaskset.1 <== total 49116169085 nsec avg 491 nsec ==> log/notaskset.2 <== total 47852147979 nsec avg 478 nsec ==> log/notaskset.3 <== total 49077846508 nsec avg 490 nsec ==> log/notaskset.4 <== total 49037126328 nsec avg 490 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 log/taskset.* ==> log/taskset.1 <== total 48534105655 nsec avg 485 nsec ==> log/taskset.2 <== total 48220818730 nsec avg 482 nsec ==> log/taskset.3 <== total 48496349690 nsec avg 484 nsec ==> log/taskset.4 <== total 48224935123 nsec avg 482 nsec Test case 2, with NO_HZ_FULL built-in but not activate in kernel cmdline: Run test program 4 times without taskset tail -n 2 nohz-log/notaskset.* ==> nohz-log/notaskset.1 <== total 48533643569 nsec avg 485 nsec ==> nohz-log/notaskset.2 <== total 47933581377 nsec avg 479 nsec ==> nohz-log/notaskset.3 <== total 49396311930 nsec avg 493 nsec ==> nohz-log/notaskset.4 <== total 48812288206 nsec avg 488 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 nohz-log/taskset.* ==> nohz-log/taskset.1 <== total 48929140711 nsec avg 489 nsec ==> nohz-log/taskset.2 <== total 48231661796 nsec avg 482 nsec ==> nohz-log/taskset.3 <== total 48482539803 nsec avg 484 nsec ==> nohz-log/taskset.4 <== total 48272541984 nsec avg 482 nsec Test case 3, with NO_HZ_FULL built-in, activate nohz_full in kernel cmdline: cat /proc/cmdline BOOT_IMAGE=/boot/vmlinuz-5.15.0-86-generic root=UUID=69036292-bdc0-4904-8724-974723f1095a ro isolcpus=2-19,22-39 nohz_full=2-19,22-39 rcu_nocbs=2-19,22-39 Run test program 4 times without taskset tail -n 2 nohz-activate-log/notaskset.* ==> nohz-activate-log/notaskset.1 <== total 52088354594 nsec avg 520 nsec ==> nohz-activate-log/notaskset.2 <== total 49226221648 nsec avg 492 nsec ==> nohz-activate-log/notaskset.3 <== total 51462517639 nsec avg 514 nsec ==> nohz-activate-log/notaskset.4 <== total 51516303613 nsec avg 515 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 nohz-activate-log/taskset.* ==> nohz-activate-log/taskset.1 <== total 56753345940 nsec avg 567 nsec ==> nohz-activate-log/taskset.2 <== total 55720022538 nsec avg 557 nsec ==> nohz-activate-log/taskset.3 <== total 55701214354 nsec avg 557 nsec ==> nohz-activate-log/taskset.4 <== total 55740784595 nsec avg 557 nsec Test case 4, with NO_HZ_FULL built-in, activate nohz_full in kernel cmdline, but run on non-activate CPU: Run test program on non-activate nohz_full CPU 20 tail -n 2 nohz-activate-off-log/* ==> nohz-activate-off-log/taskset.1 <== total 49686932587 nsec avg 496 nsec ==> nohz-activate-off-log/taskset.2 <== total 49141560622 nsec avg 491 nsec ==> nohz-activate-off-log/taskset.3 <== total 49072045557 nsec avg 490 nsec ==> nohz-activate-off-log/taskset.4 <== total 49071430182 nsec avg 490 nsec -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: s
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
On arm64 machine Hardware configs: Aarch64 128 CPUs 502G RAM, numa nodes: 4 Software configs: OS: ubuntu 20.04 Official kernel: 5.15 hwe (5.15.0-86.96~20.04.1) Test kernel: 5.15 hwe (5.15.0-86.96~20.04.1+test20231013b0) https://launchpad.net/~gerald-yang-tw/+archive/ubuntu/focal-no-hz-full Test case 1, without NO_HZ_FULL built-in (default ubuntu kernel config): Run test program 4 times without taskset tail -n 2 log/notaskset.* ==> log/notaskset.1 <== total 29370767905 nsec avg 293 nsec ==> log/notaskset.2 <== total 29359558119 nsec avg 293 nsec ==> log/notaskset.3 <== total 29370043654 nsec avg 293 nsec ==> log/notaskset.4 <== total 29362365433 nsec avg 293 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 log/taskset.* ==> log/taskset.1 <== total 29372156600 nsec avg 293 nsec ==> log/taskset.2 <== total 29367538079 nsec avg 293 nsec ==> log/taskset.3 <== total 29366224367 nsec avg 293 nsec ==> log/taskset.4 <== total 29367978392 nsec avg 293 nsec Test case 2, with NO_HZ_FULL built-in but not activate in kernel cmdline: Run test program 4 times without taskset tail -n 2 nohz-log/notaskset.* ==> nohz-log/notaskset.1 <== total 27591230003 nsec avg 275 nsec ==> nohz-log/notaskset.2 <== total 27582359987 nsec avg 275 nsec ==> nohz-log/notaskset.3 <== total 27585635138 nsec avg 275 nsec ==> nohz-log/notaskset.4 <== total 27587532170 nsec avg 275 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 nohz-log/taskset.* ==> nohz-log/taskset.1 <== total 27587206878 nsec avg 275 nsec ==> nohz-log/taskset.2 <== total 27579854104 nsec avg 275 nsec ==> nohz-log/taskset.3 <== total 27588163798 nsec avg 275 nsec ==> nohz-log/taskset.4 <== total 27589441746 nsec avg 275 nsec Test case 3, with NO_HZ_FULL built-in, activate nohz_full in kernel cmdline: cat /proc/cmdline BOOT_IMAGE=/boot/vmlinuz-5.15.0-86-generic root=UUID=7c25ee2a-4c18-462a-90db-94273e5de74b ro isolcpus=2-63,66-127 nohz_full=2-63,66-127 rcu_nocbs=2-63,66-127 sysrq_always_enabled Run test program 4 times without taskset tail -n 2 nohz-activate-log/notaskset.* ==> nohz-activate-log/notaskset.1 <== total 29986516050 nsec avg 299 nsec ==> nohz-activate-log/notaskset.2 <== total 29982386090 nsec avg 299 nsec ==> nohz-activate-log/notaskset.3 <== total 29976017400 nsec avg 299 nsec ==> nohz-activate-log/notaskset.4 <== total 29977079348 nsec avg 299 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 nohz-activate-log/taskset.* ==> nohz-activate-log/taskset.1 <== total 40561421305 nsec avg 405 nsec ==> nohz-activate-log/taskset.2 <== total 40556501183 nsec avg 405 nsec ==> nohz-activate-log/taskset.3 <== total 40554876491 nsec avg 405 nsec ==> nohz-activate-log/taskset.4 <== total 40554776851 nsec avg 405 nsec Test case 4, with NO_HZ_FULL built-in, activate nohz_full in kernel cmdline, but run on non-activate CPU: Run test program on non-activate nohz_full CPU 64 tail -n 2 nohz-activate-off-log/* ==> nohz-activate-off-log/taskset.1 <== total 29980106645 nsec avg 299 nsec ==> nohz-activate-off-log/taskset.2 <== total 29982445376 nsec avg 299 nsec ==> nohz-activate-off-log/taskset.3 <== total 29973087899 nsec avg 299 nsec ==> nohz-activate-off-log/taskset.4 <== total 29982214675 nsec avg 299 nsec -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.ser
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
On AMD EPYC 7252 Hardware configs: AMD64 32 CPUs 128G RAM, numa nodes: 2 Software configs: OS: ubuntu 20.04 Official kernel: 5.15 hwe (5.15.0-86.96~20.04.1) Test kernel: 5.15 hwe (5.15.0-86.96~20.04.1+test20231013b0) https://launchpad.net/~gerald-yang-tw/+archive/ubuntu/focal-no-hz-full Test case 1, without NO_HZ_FULL built-in (default ubuntu kernel config): Run test program 4 times without taskset tail -n 2 log/notaskset.* ==> log/notaskset.1 <== total 14800791827 nsec avg 148 nsec ==> log/notaskset.2 <== total 14800224701 nsec avg 148 nsec ==> log/notaskset.3 <== total 14995047523 nsec avg 149 nsec ==> log/notaskset.4 <== total 15056157604 nsec avg 150 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 log/taskset.* ==> log/taskset.1 <== total 14886363654 nsec avg 148 nsec ==> log/taskset.2 <== total 14954637921 nsec avg 149 nsec ==> log/taskset.3 <==
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Spend some time to get access to AMD EPYC machine For 5.15 kernel If we build NO_HZ_FULL into kernel and compare with default kernel (NO_HZ_IDLE) - on Intel machine, there is no much different - on Arm64 machine, interestingly, the context switch is a bit faster with NO_HZ_FULL built-in - on AMD EPYC machine, with NO_HZ_FUL built-in, the context switch is 3.3% worse -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Run some tests with Jammy hwe kernel (6.2.0) on AMD EPYC 7252 Test case 1, without NO_HZ_FULL built-in (default ubuntu kernel config): Run test program 4 times without taskset tail -n 2 log/notaskset.* ==> log/notaskset.1 <== total 23703299350 nsec avg 237 nsec ==> log/notaskset.2 <== total 23738030187 nsec avg 237 nsec ==> log/notaskset.3 <== total 23777052540 nsec avg 237 nsec ==> log/notaskset.4 <== total 23773975186 nsec avg 237 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 log/taskset.* ==> log/taskset.1 <== total 23817956038 nsec avg 238 nsec ==> log/taskset.2 <== total 23734814153 nsec avg 237 nsec ==> log/taskset.3 <== total 23708314067 nsec avg 237 nsec ==> log/taskset.4 <== total 23776322738 nsec avg 237 nsec Test case 2, with NO_HZ_FULL built-in but not activate in kernel cmdline: Run test program 4 times without taskset tail -n 2 nohz-log/notaskset.* ==> nohz-log/notaskset.1 <== total 24664321060 nsec avg 246 nsec ==> nohz-log/notaskset.2 <== total 24644369258 nsec avg 246 nsec ==> nohz-log/notaskset.3 <== total 24717800210 nsec avg 247 nsec ==> nohz-log/notaskset.4 <== total 24843361108 nsec avg 248 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 nohz-log/taskset.* ==> nohz-log/taskset.1 <== total 24644004125 nsec avg 246 nsec ==> nohz-log/taskset.2 <== total 24864693785 nsec avg 248 nsec ==> nohz-log/taskset.3 <== total 24745717217 nsec avg 247 nsec ==> nohz-log/taskset.4 <== total 24778959889 nsec avg 247 nsec -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
on 6.2 kernel With NO_HZ_FULL built-in, the context switch performance is ~4% worse than default config -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
The above tests is based on getpid() system call, which doesn't have much workload except context switch, so we evaluate the additional overhead caused by NO_HZ_FULL built-in on AMD EPYC machine I also used LTP to run scheduler related tests, will attach the test data later -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
The attached is ltp test results with default ubuntu kernel ** Attachment added: "log.tgz" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+attachment/5713511/+files/log.tgz -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
The attached is ltp test results with NO_HZ_FULL built-in but not actiavte ** Attachment added: "nohz-log.tgz" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+attachment/5713512/+files/nohz-log.tgz -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
The attached is ltp test results with NO_HZ_FULL built-in and activate on kernel cmdline, e.g. isolcpus=2-15,18-31 nohz_full=2-15,18-31 rcu_nocbs=2-15,18-31 tests were run on cpu 4 ** Attachment added: "nohz-log-isolcpu.tgz" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+attachment/5713513/+files/nohz-log-isolcpu.tgz -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
The attached is ltp test results with NO_HZ_FULL built-in and activate in kernel cmdline, e.g. isolcpus=2-15,18-31 nohz_full=2-15,18-31 rcu_nocbs=2-15,18-31 but tests were run on non-activate CPU 16 ** Attachment added: "nohz-log-noisolcpu.tgz" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+attachment/5713517/+files/nohz-log-noisolcpu.tgz -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Another note is that NO_HZ_FULL is already built-in on 6.5 "lowlatency" kernel: https://bugs.launchpad.net/ubuntu/+source/linux-lowlatency/+bug/2023007 But currently it's only available on Mantic, I think we should also consider if it's more proper for lowlatency kernel instead of generic -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Some observations from test results between NO_HZ_FULL built-in but not enable and default kernel Tests are from LTP scheduling related under "realtime" category And there is "no" taskset when running the tests - Gettimeofday latency (ns basis) For no_hz_full built-in: The average is almost the same, diff is 0.x ns But stddev is much higher - Pthread kill latency (us basis) For no_hz_full built-in: The average is a bit higher, 0.x - 2 us Stddev is a bit higher too - Scheduling jitter (ns basis) For no_hz_full built-in: Realtime process delta is higher, delta is the time between doing a fixed amount of work The scheduler overhead is higher? code snippet: clock_gettime(CLOCK_MONOTONIC, &start); do_work(NUMLOOPS); clock_gettime(CLOCK_MONOTONIC, &stop); /* calc delta, min and max */ delta = ts_sub(stop, start); - Scheduling latency (us basis) For no_hz_full built-in: The average is little bit higher And stddev is higher -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Gerald, Using gettimeofday for testing the effects of NO_HZ_FULL on context switch duration may not be measuring anything that changes with regards to NO_HZ_FULL. gettimeofday is implemented via VDSO, and is not an actual system call that requires a context switch. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
Thanks Jay for pointing this out! I just read the man page of vdso, it says gettimeofday is not a real system call and just read the shared memory exports by kernel. It shouldn't be used to measure the user-kernel context switch overhead caused by NO_HZ_FULL. >From what the tests does, I think scheduling jitter should be more suitable >for measuring the overhead. It measures the time of doing a fixed amount of work multiple times, if there is no additional context-switch overhead, the result should be similar under the same workloads when NO_HZ_FULL is built-in, and I didn't generate any workload on the test machine -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Status in linux source package in Jammy: In Progress Status in linux source package in Lunar: In Progress Status in linux source package in Mantic: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
** Changed in: linux (Ubuntu Focal) Status: In Progress => Won't Fix ** Changed in: linux (Ubuntu Hirsute) Status: In Progress => Won't Fix ** Changed in: linux (Ubuntu Jammy) Status: In Progress => Won't Fix ** Changed in: linux (Ubuntu Lunar) Status: In Progress => Won't Fix ** Changed in: linux (Ubuntu Mantic) Status: In Progress => Won't Fix ** Also affects: linux-lowlatency (Ubuntu) Importance: Undecided Status: New ** Changed in: linux-lowlatency (Ubuntu) Status: New => Fix Released ** Changed in: linux-lowlatency (Ubuntu Mantic) Status: New => Fix Released ** Changed in: linux-lowlatency (Ubuntu Lunar) Status: New => Won't Fix ** Changed in: linux-lowlatency (Ubuntu Jammy) Status: New => Won't Fix -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux-lowlatency package in Ubuntu: Fix Released Status in linux source package in Focal: Won't Fix Status in linux-lowlatency source package in Focal: New Status in linux source package in Groovy: Won't Fix Status in linux-lowlatency source package in Groovy: New Status in linux source package in Hirsute: Won't Fix Status in linux-lowlatency source package in Hirsute: New Status in linux source package in Jammy: Won't Fix Status in linux-lowlatency source package in Jammy: Won't Fix Status in linux source package in Lunar: Won't Fix Status in linux-lowlatency source package in Lunar: Won't Fix Status in linux source package in Mantic: Won't Fix Status in linux-lowlatency source package in Mantic: Fix Released Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
** Changed in: linux-lowlatency (Ubuntu Hirsute) Status: New => Won't Fix ** Changed in: linux-lowlatency (Ubuntu Groovy) Status: New => Won't Fix ** Changed in: linux-lowlatency (Ubuntu Focal) Status: New => Won't Fix -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux-lowlatency package in Ubuntu: Fix Released Status in linux source package in Focal: Won't Fix Status in linux-lowlatency source package in Focal: Won't Fix Status in linux source package in Groovy: Won't Fix Status in linux-lowlatency source package in Groovy: Won't Fix Status in linux source package in Hirsute: Won't Fix Status in linux-lowlatency source package in Hirsute: Won't Fix Status in linux source package in Jammy: Won't Fix Status in linux-lowlatency source package in Jammy: Won't Fix Status in linux source package in Lunar: Won't Fix Status in linux-lowlatency source package in Lunar: Won't Fix Status in linux source package in Mantic: Won't Fix Status in linux-lowlatency source package in Mantic: Fix Released Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
[Kernel-packages] [Bug 1919154] Re: Enable CONFIG_NO_HZ_FULL on supported architectures
The Groovy Gorilla has reached end of life, so this bug will not be fixed for that release ** Changed in: linux (Ubuntu Groovy) Status: In Progress => Won't Fix -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1919154 Title: Enable CONFIG_NO_HZ_FULL on supported architectures Status in linux package in Ubuntu: In Progress Status in linux source package in Focal: In Progress Status in linux source package in Groovy: Won't Fix Status in linux source package in Hirsute: In Progress Bug description: [Impact] The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid sending scheduling-clock interrupts to CPUs with a single runnable task, and such CPUs are said to be "adaptive-ticks CPUs". This is important for applications with aggressive real-time response constraints because it allows them to improve their worst-case response times by the maximum duration of a scheduling-clock interrupt. It is also important for computationally intensive short-iteration workloads: If any CPU is delayed during a given iteration, all the other CPUs will be forced to wait idle while the delayed CPU finishes. Thus, the delay is multiplied by one less than the number of CPUs. In these situations, there is again strong motivation to avoid sending scheduling-clock interrupts. [Test Plan] In order to verify the change will not cause performance issues in context switch we should compare the results for: ./stress-ng --seq 0 --metrics-brief -t 15 Running on a dedicated machine and with the following services disabled: smartd.service, iscsid.service, apport.service, cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer, fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer. The results didn't show any performance regression: https://kernel.ubuntu.com/~mhcerri/lp1919154/ [Where problems could occur] Performance degradation might happen for workloads with intensive context switching. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1919154/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
