[lkml]   [2022]   [Aug]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] sched/fair: no sync wakeup from interrupt context

On 8/3/22 02:18, Ingo Molnar wrote:
> * Libo Chen <> wrote:
>> On 8/1/22 06:26, Ingo Molnar wrote:
>>> * K Prateek Nayak <> 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: <>
>> ?? Mel was talking about a completely different thing, I brought up a
>> different patch that I wanted to revert and Mel thought it would hurt other
>> workloads which don't benefit from pulling but
>> as you can see, tbench somehow benefits from it, at least according to one
>> metric from one workload.
> Yeah - but nevertheless the discussion with Mel was open-ended AFAICS, and
> the 'major tbench regression' report by K Prateek Nayak above still stands
> and needs to be investigated/understood, right?
Oh yes, I have no issue with holding the patch back until the regression
is fully understood. I was just a little confused on your reference to
Mel's comments. Anyway, I will post my investigation soon.

> Thanks,
> Ingo

 \ /
  Last update: 2022-08-03 21:39    [W:0.127 / U:0.156 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site