linux-kernel - Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load

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Message-ID: <20160413000824.GB22643@graphite.smuckle.net>
Date:	Tue, 12 Apr 2016 17:08:24 -0700
From:	Steve Muckle <steve.muckle@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Steve Muckle <steve.muckle@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH 1/2] sched/fair: move cpufreq hook to
 update_cfs_rq_load_avg()

On Tue, Apr 12, 2016 at 04:29:06PM +0200, Rafael J. Wysocki wrote:
> This is rather fundamental.
> 
> For example, if you look at cpufreq_update_util(), it does this:
> 
> data = rcu_dereference_sched(*this_cpu_ptr(&cpufreq_update_util_data));
> 
> meaning that it will run the current CPU's utilization update
> callback.  Of course, that won't work cross-CPU, because in principle
> different CPUs may use different governors and therefore different
> util update callbacks.

Will something like the attached (unfinished patches) work? It seems
to for me, but I haven't tested it much beyond confirming the hook is
working on remote wakeups.

I'm relying on the previous comment that it's up to cpufreq drivers to
run stuff on the target policy's CPUs if the driver needs that.

There's still some more work, fixing up some more smp_processor_id()
usage in schedutil, but it should be easy (trace, slow path irq_work
target).

> If you want to do remote updates, I guess that will require an
> irq_work to run the update on the target CPU, but then you'll probably
> want to neglect the rate limit on it as well, so it looks like a
> "need_update" flag in struct update_util_data will be useful for that.

Why is it required to run the update on the target CPU?

thanks,
Steve

View attachment "0001-sched-cpufreq_sched-remove-smp_processor_id-usage.patch" of type "text/x-diff" (2143 bytes)

View attachment "0002-sched-fair-call-cpufreq-hook-for-remote-wakeups.patch" of type "text/x-diff" (2876 bytes)