Messages in this thread | | | Date | Mon, 4 Sep 2023 20:59:03 -0700 | Subject | Re: [PATCH v2] freezer,sched: Use saved_state to reduce some spurious wakeups | From | Elliot Berman <> |
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On 9/4/2023 2:23 PM, Peter Zijlstra wrote: > On Wed, Aug 30, 2023 at 10:42:39AM -0700, Elliot Berman wrote: > >> Avoid the spurious wakeups by saving the state of TASK_FREEZABLE tasks. >> If the task was running before entering TASK_FROZEN state >> (__refrigerator()) or if the task received a wake up for the saved >> state, then the task is woken on thaw. saved_state from PREEMPT_RT locks >> can be re-used because freezer would not stomp on the rtlock wait flow: >> TASK_RTLOCK_WAIT isn't considered freezable. > > You don't actually assert that anywhere I think, so the moment someone > makes that happen you crash and burn. >
I can certainly add an assertion on the freezer side.
> Also: > >> -#ifdef CONFIG_PREEMPT_RT >> +#if IS_ENABLED(CONFIG_PREEMPT_RT) || IS_ENABLED(CONFIG_FREEZER) > > That makes wakeup more horrible for everyone :/
I don't think the hot wakeup path is significantly impacted because the added checks come after the hot path is already not taken.
wait_task_inactive() is impacted in the case of contention on pi_lock, but I don't think that is part of any hot path.
I'll run some further tests on my end to be sure about the wake up latency. Are there any benchmarks/tests you like for measuring the hot path? I can run those as well.
Thanks, Elliot
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