linux-kernel - Re: [PATCH v3 1/4] sched: cgroup SCHED

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Date:   Tue, 24 Aug 2021 06:45:44 +0800
From:   Tao Zhou <tao.zhou@...ux.dev>
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>, tao.zhou@...ux.dev
Subject: Re: [PATCH v3 1/4] sched: cgroup SCHED_IDLE support

Hi Josh,

On Mon, Aug 23, 2021 at 10:29:53AM -0700, Josh Don wrote:
> Hi Tao,
> 
> On Fri, Aug 20, 2021 at 1:38 AM Tao Zhou <tao.zhou@...ux.dev> wrote:
> [snip]
> > >  #ifdef CONFIG_SMP
> > >  extern void set_task_rq_fair(struct sched_entity *se,
> > >                            struct cfs_rq *prev, struct cfs_rq *next);
> > > @@ -601,6 +606,9 @@ struct cfs_rq {
> > >       struct list_head        leaf_cfs_rq_list;
> > >       struct task_group       *tg;    /* group that "owns" this runqueue */
> > >
> > > +     /* Locally cached copy of our task_group's idle value */
> > > +     int                     idle;
> > > +
> > >  #ifdef CONFIG_CFS_BANDWIDTH
> > >       int                     runtime_enabled;
> > >       s64                     runtime_remaining;
> > > --
> > > 2.33.0.rc2.250.ged5fa647cd-goog
> > >
> >
> > Cfs_rq and tg define @idle with int type.
> > In sched_group_set_idle(..., long idle), @idle is long type.
> > Use int instead.
> >
> > But, you filter idle value:
> >
> >     if (idle < 0 || idle > 1)
> >         return -EINVAL;
> >
> > So, no effect here.. Just @idle can use 4 bytes.
> >
> >
> >
> > Thanks,
> > Tao
> 
> The use of 'long'  there is because the input from the cgroup
> interface is a 64 bit value.

Yes. If the compile align the stack to 8 or other, this will have 
no effect(I've not check this, and have not much about gcc compile
align). I just presume that if the stack can save 4 bytes. But, 
that may not right though.

> - Josh



Thanks,
Tao