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 <== total 14784359811 nsec avg 147 nsec ==> log/taskset.4 <== total 14971006444 nsec avg 149 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-log1/notaskset.1 <== total 15481330071 nsec avg 154 nsec ==> nohz-log1/notaskset.2 <== total 15336097628 nsec avg 153 nsec ==> nohz-log1/notaskset.3 <== total 15465283005 nsec avg 154 nsec ==> nohz-log1/notaskset.4 <== total 15575165790 nsec avg 155 nsec Run test program 4 times with taskset to CPU 4 tail -n 2 nohz-log1/taskset.* ==> nohz-log1/taskset.1 <== total 15492308210 nsec avg 154 nsec ==> nohz-log1/taskset.2 <== total 15481404702 nsec avg 154 nsec ==> nohz-log1/taskset.3 <== total 15386525422 nsec avg 153 nsec ==> nohz-log1/taskset.4 <== total 15393744615 nsec avg 153 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
