linux-kernel - Re: Remove WQ_CPU_INTENSIVE flag from unbound wq's

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Message-ID: <CAPhsuW70_HtmxA0qmUVLk4L+Ls5t=0j0k5D4fbT4fNY59L2UpQ@mail.gmail.com>
Date:   Thu, 13 Feb 2020 15:42:45 -0800
From:   Song Liu <song@...nel.org>
To:     Maksym Planeta <mplaneta@...inf.tu-dresden.de>
Cc:     Mike Snitzer <snitzer@...hat.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Alasdair Kergon <agk@...hat.com>, dm-devel@...hat.com,
        Gao Xiang <xiang@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-crypto@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        linux-raid <linux-raid@...r.kernel.org>,
        linux-erofs@...ts.ozlabs.org
Subject: Re: Remove WQ_CPU_INTENSIVE flag from unbound wq's

On Thu, Feb 13, 2020 at 8:19 AM Maksym Planeta
<mplaneta@...inf.tu-dresden.de> wrote:
>
>
>
> On 13/02/2020 16:36, Mike Snitzer wrote:
> > On Thu, Feb 13 2020 at  9:18am -0500,
> > Maksym Planeta <mplaneta@...inf.tu-dresden.de> wrote:
> >
> >> The documentation [1] says that WQ_CPU_INTENSIVE is "meaningless" for
> >> unbound wq. I remove this flag from places where unbound queue is
> >> allocated. This is supposed to improve code readability.
> >>
> >> 1. https://www.kernel.org/doc/html/latest/core-api/workqueue.html#flags
> >>
> >> Signed-off-by: Maksym Planeta <mplaneta@...inf.tu-dresden.de>
> >
> > What the Documentation says aside, have you cross referenced with the
> > code?  And/or have you done benchmarks to verify no changes?
> >
>
> It seems so from the code. Although, I'm not 100% confident. I did not
> run benchmarks, instead I relied that on the assumption that
> documentation is correct.

>From the code, WQ_CPU_INTENSIVE is only used to set
WORKER_CPU_INTENSIVE, and WORKER_CPU_INTENSIVE is only used
as part of WORKER_NOT_RUNNING, which includes WORKER_UNBOUND.
So, I agree that with current code, WQ_CPU_INTENSIVE with WQ_UNBOUND
is same as WQ_UNBOUND alone.

However, I don't think it is necessary to make the changes. They don't really
improve readability of the code.

Thanks,
Song