linux-kernel - Re: [PATCH v2 1/2] cpufreq / sched: Pass flags to cpufreq_update

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Date:   Mon, 22 Aug 2016 19:30:36 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Steve Muckle <steve.muckle@...aro.org>,
        Juri Lelli <juri.lelli@....com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2 1/2] cpufreq / sched: Pass flags to cpufreq_update_util()

On Saturday, August 20, 2016 05:40:49 PM Krzysztof Kozlowski wrote:
> On Sat, Aug 20, 2016 at 03:08:01AM +0200, Rafael J. Wysocki wrote:
> > On Friday, August 19, 2016 03:26:21 PM Krzysztof Kozlowski wrote:
> > > On Fri, Aug 12, 2016 at 2:04 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > >
> > > > It is useful to know the reason why cpufreq_update_util() has just
> > > > been called and that can be passed as flags to cpufreq_update_util()
> > > > and to the ->func() callback in struct update_util_data.  However,
> > > > doing that in addition to passing the util and max arguments they
> > > > already take would be clumsy, so avoid it.
> > > >
> > > > Instead, use the observation that the schedutil governor is part
> > > > of the scheduler proper, so it can access scheduler data directly.
> > > > This allows the util and max arguments of cpufreq_update_util()
> > > > and the ->func() callback in struct update_util_data to be replaced
> > > > with a flags one, but schedutil has to be modified to follow.
> > > >
> > > > Thus make the schedutil governor obtain the CFS utilization
> > > > information from the scheduler and use the "RT" and "DL" flags
> > > > instead of the special utilization value of ULONG_MAX to track
> > > > updates from the RT and DL sched classes.  Make it non-modular
> > > > too to avoid having to export scheduler variables to modules at
> > > > large.
> > > >
> > > > Next, update all of the other users of cpufreq_update_util()
> > > > and the ->func() callback in struct update_util_data accordingly.
> > > >
> > > > Suggested-by: Peter Zijlstra <peterz@...radead.org>
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > ---
> > > >
> > > > v1 -> v2: Do not check cpu_of(rq) against smp_processor_id() in
> > > >           cfs_rq_util_change().
> > > >
> > > > ---
> > > >  drivers/cpufreq/Kconfig            |    5 --
> > > >  drivers/cpufreq/cpufreq_governor.c |    2 -
> > > >  drivers/cpufreq/intel_pstate.c     |    2 -
> > > >  include/linux/sched.h              |   12 ++++--
> > > >  kernel/sched/cpufreq.c             |    2 -
> > > >  kernel/sched/cpufreq_schedutil.c   |   67 ++++++++++++++++++++-----------------
> > > >  kernel/sched/deadline.c            |    4 +-
> > > >  kernel/sched/fair.c                |   10 +----
> > > >  kernel/sched/rt.c                  |    4 +-
> > > >  kernel/sched/sched.h               |   31 +++++------------
> > > >  10 files changed, 66 insertions(+), 73 deletions(-)
> > > 
> > > (...)
> > > 
> > > > --- linux-pm.orig/drivers/cpufreq/Kconfig
> > > > +++ linux-pm/drivers/cpufreq/Kconfig
> > > > @@ -194,7 +194,7 @@ config CPU_FREQ_GOV_CONSERVATIVE
> > > >           If in doubt, say N.
> > > >
> > > >  config CPU_FREQ_GOV_SCHEDUTIL
> > > > -       tristate "'schedutil' cpufreq policy governor"
> > > > +       bool "'schedutil' cpufreq policy governor"
> > > 
> > > If you change such symbols please remember to update also all the
> > > defconfigs. Without the update they start to show errors.
> > 
> > Are there defconfigs that use this particular one?
> 
> Yes, ARM/multi_v7 and exynos were using this as module. Javier sent a
> patch for that and should be switched to builtin in upcoming next [1].
> 
> If you would like to base on top of that, let me know, so I would
> prepare a tag.

I wouldn't like to rebase, but I can pull that branch depending on how
much more material there is on it.

Thanks,
Rafael