linux-kernel - Re: [PATCH v9 09/15] sched: Introduce sched_energy

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Date:   Thu, 22 Nov 2018 15:55:27 +0000
From:   Quentin Perret <quentin.perret@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Chris Redpath <chris.redpath@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Steve Muckle <smuckle@...gle.com>, adharmap@...eaurora.org,
        Saravana Kannan <skannan@...eaurora.org>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        currojerez@...eup.net, Javi Merino <javi.merino@...nel.org>
Subject: Re: [PATCH v9 09/15] sched: Introduce sched_energy_present static key

On Thursday 22 Nov 2018 at 16:51:41 (+0100), Rafael J. Wysocki wrote:
> On Thu, Nov 22, 2018 at 4:25 PM Quentin Perret <quentin.perret@....com> wrote:
> >
> > On Thursday 22 Nov 2018 at 11:25:45 (+0100), Peter Zijlstra wrote:
> > > On Thu, Nov 22, 2018 at 09:32:39AM +0000, Quentin Perret wrote:
> > > > Hmm, I went too fast, that's totally broken. But there's still something
> > > > we can do with static_branch_{inc,dec} I think. I'll come back later
> > > > with a better solution.
> > >
> > > Right; if you count the rd's that have pd set, it should work-ish. Yes,
> > > much cleaner if you can get it to work.
> >
> > So, I came up with the following code which seems to work OK. It's not
> > as I clean as I'd like, though. The fact that free_pd() can be called in
> > softirq context is annoying to manipulate the static key ...
> >
> > An alternative to this work item workaround is to do static_branch_dec()
> > from build_perf_domains() and next to the three call sites of
> > free_rootdomain() in order to avoid the call_rcu() context. Not very
> > pretty either.
> >
> > Or we can just stick with your original suggestion to carry a boolean
> > around.
> 
> What's problematic with carrying a boolean around?

Nothing, I was just trying to see if I could find a more elegant way to
increment/decrement the static key as we create/destroy the perf
domains.

I would not describe the work item thing I came up with as particularly
elegant, though :-)

So, all in all, the boolean is fine by me if we all agree it is nicer.

Thanks,
Quentin