linux-kernel - Re: [PATCH v3 3/4] sched: reduce sched slice for SCHED

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAPJCdBk-8vjg6GtGx3ft3KoyeeXvovxF53kwE7vJGY2eTYOwyg@mail.gmail.com>
Date:   Wed, 25 Aug 2021 10:43:56 +0800
From:   Jiang Biao <benbjiang@...il.com>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Paul Turner <pjt@...gle.com>,
        Oleg Rombakh <olegrom@...gle.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Steve Sistare <steven.sistare@...cle.com>,
        Tejun Heo <tj@...nel.org>, Rik van Riel <riel@...riel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] sched: reduce sched slice for SCHED_IDLE entities

On Wed, 25 Aug 2021 at 01:04, Josh Don <joshdon@...gle.com> wrote:
>
> Hi Jiang,
>
> On Tue, Aug 24, 2021 at 3:25 AM Jiang Biao <benbjiang@...il.com> wrote:
> >
> > Why not just ignore min granularity when normal entities compete with
> > a SCHED_IDLE entity? something like this,
> >
> > @@ -697,8 +710,14 @@ static u64 sched_slice(struct cfs_rq *cfs_rq,
> > struct sched_entity *se)
> >                  slice = __calc_delta(slice, se->load.weight, load);
> >          }
> >
> >  -       if (sched_feat(BASE_SLICE))
> >  -               slice = max(slice, (u64)sysctl_sched_min_granularity);
> >  +       if (sched_feat(BASE_SLICE)
> >  +          && (!se_is_idle(init_se) || sched_idle_cfs_rq(cfs_rq)))
> >  +               slice = max(slice, (u64)sysctl_sched_min_granularity);
> >
> >          return slice;
> >   }
> > If so, there seems no need to introduce sysctl_sched_idle_min_granularity? :)
>
> Ignoring min_gran entirely could lead to some really tiny slices; see
> discussion at https://lkml.org/lkml/2021/8/12/651.
Got it, tiny slices could be a problem in SCHED_HRTICK case.
But the sysctl_sched_idle_min_granularity used in sched_slice() and
sysctl_sched_min_granularity used in check_preempt_tick would have
different semantics for SCHED_IDLE task, which could be functional ok
but a little confusing.

Regards,
Jiang