Messages in this thread | | | Date | Fri, 6 Oct 2023 10:35:43 +0530 | Subject | Re: [PATCH v8 00/25] timer: Move from a push remote at enqueue to a pull at expiry model | From | K Prateek Nayak <> |
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Hello Anna-Maria,
On 10/4/2023 6:04 PM, Anna-Maria Behnsen wrote: > [..snip..] > > Ping Pong Oberservation > ^^^^^^^^^^^^^^^^^^^^^^^ > > During testing on a mostly idle machine a ping pong game could be observed: > a process_timeout timer is expired remotely on a non idle CPU. Then the CPU > where the schedule_timeout() was executed to enqueue the timer comes out of > idle and restarts the timer using schedule_timeout() and goes back to idle > again. This is due to the fair scheduler which tries to keep the task on > the CPU which it previously executed on.
Regarding above, are you referring to "wake_up_process(timeout->task)" in "process_timeout()" ends up waking the task on an idle CPU instead of the CPU where process_timeout() ran?
In which case, have you tried using the "WF_CURRENT_CPU" flag for the wakeup? (landed upstream in v6.6-rc1) It is only used by wait queues in kernel/sched/wait.c currently but perhaps we can have a "wake_up_process_on_current_cpu()" that process_timeout() can call.
Something along the lines of:
int wake_up_process_on_current_cpu(struct task_struct *p) { return try_to_wake_up(p, TASK_NORMAL, WF_CURRENT_CPU); } EXPORT_SYMBOL(wake_up_process_on_current_cpu);
Thoughts?
> > [..snip..] >
-- Thanks and Regards, Prateek
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