linux-kernel - Re: [RFC PATCH] sched: fix the nonsense shares when load of cfs

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: <CAKfTPtD+He8UULUavz0csUeUV3TBdjShV9kUPQY6rpLswUAm4g@mail.gmail.com>
Date:   Fri, 6 Mar 2020 09:04:45 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     王贇 <yun.wang@...ux.alibaba.com>
Cc:     Ben Segall <bsegall@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        "open list:SCHEDULER" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] sched: fix the nonsense shares when load of cfs_rq is
 too, small

On Fri, 6 Mar 2020 at 05:23, 王贇 <yun.wang@...ux.alibaba.com> wrote:
>
>
>
> On 2020/3/5 下午3:53, Vincent Guittot wrote:
> > On Thu, 5 Mar 2020 at 02:14, 王贇 <yun.wang@...ux.alibaba.com> wrote:
> [snip]
> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >>> index fcc968669aea..6d7a9d72d742 100644
> >>> --- a/kernel/sched/fair.c
> >>> +++ b/kernel/sched/fair.c
> >>> @@ -3179,9 +3179,9 @@ static long calc_group_shares(struct cfs_rq *cfs_rq)
> >>>         long tg_weight, tg_shares, load, shares;
> >>>         struct task_group *tg = cfs_rq->tg;
> >>>
> >>> -       tg_shares = READ_ONCE(tg->shares);
> >>> +       tg_shares = scale_load_down(READ_ONCE(tg->shares));
> >>>
> >>> -       load = max(scale_load_down(cfs_rq->load.weight), cfs_rq->avg.load_avg);
> >>> +       load = max(cfs_rq->load.weight, scale_load(cfs_rq->avg.load_avg));
> >>>
> >>>         tg_weight = atomic_long_read(&tg->load_avg);
> >>
> >> Get the point, but IMHO fix scale_load_down() sounds better, to
> >> cover all the similar cases, let's first try that way see if it's
> >> working :-)
> >
> > The problem with this solution is that the avg.load_avg of gse or
> > cfs_rq might stay to 0 because it uses
> > scale_load_down(se/cfs_rq->load.weight)
>
> Will cfs_rq->load.weight be zero too without scale down?

cfs_rq->load.weight will never be 0, it's min is 2

>
> If cfs_rq->load.weight got at least something, the load will not be
> zero after pick the max, correct?

But the cfs_rq->avg.load_avg will never be other than 0 what ever
there are heavy or light tasks in the group

>
> Regards,
> Michael Wang
>
> >
> >>
> >> Regards,
> >> Michael Wang
> >>
> >>>
> >>>
> >>>