Messages in this thread Patch in this message | | | From | chi wu <> | Date | Mon, 20 Mar 2023 20:40:51 +0800 | Subject | Re: [PATCH] sched/core: Reduce cost of sched_move_task when config autogroup |
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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?
@@ -10369,6 +10390,9 @@ void sched_move_task(struct task_struct *tsk) rq = task_rq_lock(tsk, &rf);
+ if (!sched_task_group_changed(tsk)) + goto unlock; + update_rq_clock(rq);
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