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Date: Tue, 9 Sep 2014 11:56:18 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Anup Chenthamarakshan <anupc@...omium.org>
Cc: Dirk Brandewie <dirk.j.brandewie@...el.com>,
Sameer Nanda <snanda@...omium.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] intel_pstate: track and export frequency residency stats
via sysfs.
On Tue, Sep 9, 2014 at 11:02 AM, Anup Chenthamarakshan
<anupc@...omium.org> wrote:
> I had initially tried reusing cpufreq_stats.c to export stats.
> Calling cpufreq_stats_update() via the cpufreq notifier added
> some amount of overhead while switching frequencies. Specifically,
> looking up the index of the new frequency in freq_table_get_index()
> is a linear search through all available frequencies (vs a single
> subtraction with custom stats export). Also, the notifier mechanism
I don't think just this linear search will make things so bad..
> itself added a level of indirection before calling stats_update.
Probably some other notifier is registered which is taking considerable
amount of time.. Try checking what all registered with cpufreq-core.
> There is a 5X increase in time taken to complete intel_pstate_set_pstate
> while using cpufreq_stats compared to having custom stats exported.
Try calling cpufreq_stat_notifier_trans() directly instead of a notifier
and lets see if this makes it any better.
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