Re: [PATCH v4 0/2] Avoid spurious freezer wakeups

[Peter Zijlstra]

On Tue, Sep 26, 2023 at 04:17:33PM +0000, Carlos Llamas wrote:
> On Fri, Sep 08, 2023 at 03:49:14PM -0700, Elliot Berman wrote:
> > After commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic"),
> > tasks that transition directly from TASK_FREEZABLE to TASK_FROZEN  are
> > always woken up on the thaw path. Prior to that commit, tasks could ask
> > freezer to consider them "frozen enough" via freezer_do_not_count(). The
> > commit replaced freezer_do_not_count() with a TASK_FREEZABLE state which
> > allows freezer to immediately mark the task as TASK_FROZEN without
> > waking up the task.  This is efficient for the suspend path, but on the
> > thaw path, the task is always woken up even if the task didn't need to
> > wake up and goes back to its TASK_(UN)INTERRUPTIBLE state. Although
> > these tasks are capable of handling of the wakeup, we can observe a
> > power/perf impact from the extra wakeup.
> 
> This issue is hurting the performance of our stable 6.1 releases. Does
> it make sense to backport these patches into stable branches once they
> land in mainline? I would assume we want to fix the perf regression
> there too?

Note that these patches are in tip/sched/core, slated for the next merge
window.