linux-kernel - Re: [PATCH 4/6] psi: introduce state_mask to represent stalled psi states

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Date:   Mon, 17 Dec 2018 17:14:53 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, lizefan@...wei.com,
        Johannes Weiner <hannes@...xchg.org>, axboe@...nel.dk,
        dennis@...nel.org, Dennis Zhou <dennisszhou@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, cgroups@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com
Subject: Re: [PATCH 4/6] psi: introduce state_mask to represent stalled psi states

On Mon, Dec 17, 2018 at 7:55 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Dec 14, 2018 at 09:15:06AM -0800, Suren Baghdasaryan wrote:
> > The psi monitoring patches will need to determine the same states as
> > record_times(). To avoid calculating them twice, maintain a state mask
> > that can be consulted cheaply. Do this in a separate patch to keep the
> > churn in the main feature patch at a minimum.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> >  include/linux/psi_types.h |  3 +++
> >  kernel/sched/psi.c        | 29 +++++++++++++++++++----------
> >  2 files changed, 22 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
> > index 2cf422db5d18..2c6e9b67b7eb 100644
> > --- a/include/linux/psi_types.h
> > +++ b/include/linux/psi_types.h
> > @@ -53,6 +53,9 @@ struct psi_group_cpu {
> >       /* States of the tasks belonging to this group */
> >       unsigned int tasks[NR_PSI_TASK_COUNTS];
> >
> > +     /* Aggregate pressure state derived from the tasks */
> > +     u32 state_mask;
> > +
> >       /* Period time sampling buckets for each state of interest (ns) */
> >       u32 times[NR_PSI_STATES];
> >
>
> Since we spend so much time counting space in that line, maybe add a
> note to the Changlog about how this fits.

Will do.

> Also, since I just had to re-count, you might want to add explicit
> numbers to the psi_res and psi_states enums.

Sounds reasonable.

> > +             if (state_mask & (1 << s))
>
> We have the BIT() macro, but I'm honestly not sure that will improve
> things.

I was mimicking the rest of the code in psi.c that uses this kind of
bit masking. Can change if you think that would be better.