Re: [PATCH] intel_pstate: track and export frequency residency stats via sysfs.

[Viresh Kumar]

On Tue, Sep 9, 2014 at 11:02 AM, Anup Chenthamarakshan
<anupc@xxxxxxxxxxxx> 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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