linux-kernel - Re: [PATCH v3 linux-next] cpufreq: ondemand: Calculate gradient of CPU load to early increase frequency

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Date:	Thu, 4 Apr 2013 10:24:40 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stratos Karafotis <stratosk@...aphore.gr>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 linux-next] cpufreq: ondemand: Calculate gradient of
 CPU load to early increase frequency

Hi Stratos,

On 4 April 2013 05:00, Stratos Karafotis <stratosk@...aphore.gr> wrote:
> I tried to do some measurements simulating a CPU load with a loop that simply counts
> an integer. The first test simulates a CPU load that lasts 2 x sampling_rate = ~ 20000us.
> The second ~40000us and the third ~60000us.
> There are 5 runs in each test. In each run the benchmark program counts 20 times with
> early_demand off and 20 times with early_demand on and takes the average times.
>
> I run the benchmark program on 3.9-rc5 + early_demand patch. My CPU is the i7-3770 @ 3.40 GHz
>
> Please find below the results, and the benchmark code attached.
> Please note, that the idea of this patch is to push the CPU to max frequency few sampling
> periods (1 in most cases) earlier for a more responsive system.

Yes, your results show some improvements. BUT if performance is the only thing
we were looking for, then we will never use ondemand governor but performance
governor.

I suspect this little increase in performance must have increased power numbers
too (significantly). So, if you can get numbers in the form of power/performance
with and without your patch, it will be great.

--
viresh
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