linux-kernel - Re: [PATCH 3/3 v4] cpufreq: governor: Replace timers with utilization update callbacks

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Message-ID: <20160207092019.GB6112@vireshk>
Date:	Sun, 7 Feb 2016 14:50:19 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
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>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3 v4] cpufreq: governor: Replace timers with
 utilization update callbacks

On 06-02-16, 04:40, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Instead of using a per-CPU deferrable timer for queuing up governor
> work items, register a utilization update callback that will be
> invoked from the scheduler on utilization changes.
> 
> The sampling rate is still the same as what was used for the
> deferrable timers and the added irq_work overhead should be offset by
> the eliminated timers overhead, so in theory the functional impact of
> this patch should not be significant.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> Updated after the recent discussion with Viresh.
> 
> Changes from v3:
> - The completion used for irq_work synchronization replaced with irq_work_sync()
>   in gov_cancel_work().
> - update_sampling_rate() now modifies shared->sample_delay_ns for all CPUs
>   where it matters directly with a big fat comment explaining why this is
>   actually OK.
> - The above means the time_stamp field in struct cpu_common_dbs_info is not
>   necessary any more, so it is dropped.
> - A build error for !CONFIG_SMP is addressed (hopefully effectively).
> 
> This version was lightly tested on an x86 laptop.

Awesome work Rafael, this looks really good now.

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh