linux-kernel - Re: [PATCH v10 1/3] cpufreq: Add mechanism for registering utilization update callbacks

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Message-ID: <20160309123539.GL6356@twins.programming.kicks-ass.net>
Date:	Wed, 9 Mar 2016 13:35:39 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v10 1/3] cpufreq: Add mechanism for registering
 utilization update callbacks

On Mon, Feb 15, 2016 at 10:47:22PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Introduce a mechanism by which parts of the cpufreq subsystem
> ("setpolicy" drivers or the core) can register callbacks to be
> executed from cpufreq_update_util() which is invoked by the
> scheduler's update_load_avg() on CPU utilization changes.
> 
> This allows the "setpolicy" drivers to dispense with their timers
> and do all of the computations they need and frequency/voltage
> adjustments in the update_load_avg() code path, among other things.
> 
> The update_load_avg() changes were suggested by Peter Zijlstra.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/cpufreq.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/cpufreq.h   |   34 ++++++++++++++++++++++++++++++++++
>  kernel/sched/deadline.c   |    4 ++++
>  kernel/sched/fair.c       |   26 +++++++++++++++++++++++++-
>  kernel/sched/rt.c         |    4 ++++
>  kernel/sched/sched.h      |    1 +
>  6 files changed, 113 insertions(+), 1 deletion(-)
> 

So with the understanding that we'll work on getting rid of
cpufreq_trigger_update().

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Also, Vincent had some concerns about the exact placement of the
callback, and I see no problem in moving it if there's need.