Re: [PATCH] sched/fair: no sync wakeup from interrupt context

Ingo Molnar
2022-08-01T13:26:48Z

* K Prateek Nayak <kprateek.nayak@amd.com> wrote:

> Hello Libo and Peter,
>
> tl;dr
>
> - We observed a major regression with tbench when testing the latest tip
> sched/core at:
> commit 14b3f2d9ee8d "sched/fair: Disallow sync wakeup from interrupt context"
> Reason for the regression are the fewer affine wakeups that leaves the
> client farther away from the data it needs to consume next primed in the
> waker's LLC.
> Such regressions can be expected from tasks that use sockets to communicate
> significant amount of data especially on system with multiple LLCs.
>
> - Other benchmarks have a comparable behavior to the tip at previous commit
> commit : 91caa5ae2424 "sched/core: Fix the bug that task won't enqueue
> into core tree when update cookie"
>
> I'll leave more details below.

Mel Gorman also warned about this negative side-effect in:

Subject: Re: [PATCH] sched/fair: no sync wakeup from interrupt context
Date: Fri, 15 Jul 2022 11:07:38 +0100
Message-ID: <20220715100738.GD3493@suse.de>

https://lore.kernel.org/all/20220715100738.GD3493@suse.de/

I've reverted this commit (14b3f2d9ee8df3b) for the time being from
tip:sched/core.

Thanks for the heads-up!

Thanks,

Ingo