Messages in this thread | | | Date | Mon, 20 Mar 2023 16:13:31 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched/core: Reduce cost of sched_move_task when config autogroup |
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On Mon, Mar 20, 2023 at 08:40:51PM +0800, chi wu wrote: > Peter Zijlstra <peterz@infradead.org> 于2023年3月20日周一 16:28写道: > > > > On Sun, Mar 19, 2023 at 03:56:43PM +0800, wuchi wrote: > > > Some sched_move_task calls of autogroup is useless when the > > > task_struct->sched_task_group isn't changed because of task_group > > > of cpu_cgroup overlay task_group of autogroup. The overlay key codes > > > are as follows: > > > > > > sched_cgroup_fork->autogroup_task_group->task_wants_autogroup > > > sched_change_group->autogroup_task_group->autogroup_task_group > > > > > > sched_move_task eg: > > > task A belongs to cpu_cgroup0 and autogroup0, it will always to > > > cpu_cgroup0 when doing exit. So there is no need to do {de|en}queue. > > > The call graph is as follow. > > > > > > do_exit > > > sched_autogroup_exit_task > > > sched_move_task > > > dequeue_task > > > sched_change_group > > > A.sched_task_group = sched_get_task_group > > > enqueue_task > > > > > > So do some check before dequeue task in sched_move_task. > > > > No immediate objection; but the $subject seems to suggest you did this > > for performance reasons, yet there are no performance results in this > > Changelog. How much does this save under what load? > > cpu:bogomips=4600.00 > kernel:6.3.0-rc3 > cpu cgroup: 6:cpu,cpuacct:/user.slice > > run cmds: > > #!/bin/bash > for i in {0..10000}; do > sleep 0 & > done > wait > > bpftrace -e 'k:sched_move_task { @ts[tid] = nsecs; } > kr:sched_move_task /@ts[tid]/ { @ns += nsecs - @ts[tid]; > delete(@ts[tid]); }' > > cost time(ns): > without patch: 43528033 > with patch: 18934496 > diff: -24593537 -56.5% > > About the change, move sched_task_group_changed before > update_rq_clock as following and add the performance results in > the Changelog?
Yes please, that gives good motivation for the change.
Thanks!
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