linux-kernel - Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update

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Date:	Wed, 16 Mar 2016 14:43:38 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Juri Lelli <Juri.Lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Michael Turquette <mturquette+renesas@...libre.com>
Subject: Re: [PATCH 5/8] sched/cpufreq: pass sched class into
 cpufreq_update_util

On Wed, Mar 16, 2016 at 02:23:21PM +0100, Rafael J. Wysocki wrote:
> On Wed, Mar 16, 2016 at 2:10 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > (this would of course require we allocate struct update_util_data with
> > the proper alignment thingies etc..)

> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index ba49c9efd0b2..d34d75c5cc93 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -3236,8 +3236,10 @@ static inline unsigned long rlimit_max(unsigned int limit)
> >
> >  #ifdef CONFIG_CPU_FREQ
> >  struct update_util_data {
> > -       void (*func)(struct update_util_data *data,
> > -                    u64 time, unsigned long util, unsigned long max);
> > +       unsigned long *cfs_util_avg;
> > +       unsigned long *cfs_util_max;
> > +
> > +       void (*func)(struct update_util_data *data, u64 time);
> >  };

we should add: ____cacheline_aligned here

> How do we ensure proper alignment?

Depends on the allocator; not all of them respect the struct alignment
attribute.

kernel/sched/cpufreq.c:DEFINE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);

That one could use:

DEFINE_PER_CPU_ALIGNED() instead

as would this one:

drivers/cpufreq/cpufreq_governor.c:static DEFINE_PER_CPU(struct cpu_dbs_info, cpu_dbs);

Because when you cacheline align dbs_info, its update_util_data member
will also get the correct alignment because of the structure attribute.