linux-kernel - Re: [PATCH v2] sched/isolation: add a workqueue parameter to constrain unbound CPUs

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Message-ID: <CAEQmJ=jW7O=EVQC7UxGSX+YDK8aTTcF3gje5HgwuTY9cnE0C2g@mail.gmail.com>
Date:   Thu, 22 Jun 2023 11:47:06 +0800
From:   Yuanhan Zhang <zyhtheonly@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.co,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        fuyuanli@...iglobal.com, zwp10758@...il.com, zyhtheonly@...h.net
Subject: Re: [PATCH v2] sched/isolation: add a workqueue parameter to
 constrain unbound CPUs

Tejun Heo <tj@...nel.org> 于2023年6月22日周四 04:51写道：
>
> On Wed, Jun 14, 2023 at 05:19:45PM +0800, tiozhang wrote:
> ...
> > @@ -181,8 +181,8 @@ static int __init housekeeping_nohz_full_setup(char *str)
> >  {
> >       unsigned long flags;
> >
> > -     flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
> > -             HK_FLAG_MISC | HK_FLAG_KTHREAD;
> > +     flags = HK_FLAG_TICK | HK_FLAG_TIMER | HK_FLAG_RCU | HK_FLAG_MISC
> > +             | HK_FLAG_KTHREAD;
>
> Why is WQ being taken out of nohz_full setup? The patch description doesn't
> mention anything.

To prevent nohz_full from rewriting workqueue's choice. Add a
description in patch v3.

>
> > @@ -208,6 +208,12 @@ static int __init housekeeping_isolcpus_setup(char *str)
> >                       continue;
> >               }
> >
> > +             if (!strncmp(str, "workqueue,", 10)) {
> > +                     str += 10;
> > +                     flags |= HK_FLAG_WQ;
> > +                     continue;
> > +             }
>
> I wonder whether it'd be better to just add a workqueue boot param but if

I also write a patch this way, please see '[PATCH] workqueue: add
cmdline parameter
`unbound_workqueue_cpus` to further constrain wq_unbound_cpumask at boot time'.
If you think it is better I'm happy to continue on this :)

> this works it's fine too.

It works since we use this cpumask to constrain wq_unbound_cpumask in
workqueue's early init.

>
> Thanks.
>
> --
> tejun

Thank you,
tiozhang