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: 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
