linux-kernel - Re: [PATCH v3 1/3] cpufreq: ondemand: Change the calculation of target frequency

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Date:	Thu, 06 Jun 2013 15:56:46 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Borislav Petkov <bp@...e.de>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-pm@...r.kernel.org,
	cpufreq@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] cpufreq: ondemand: Change the calculation of
 target frequency

Thanks Viresh. I think I couldn't explain this in better way.
Also thanks for acknowledgment!

Stratos

Viresh Kumar <viresh.kumar@...aro.org> wrote:

>On 6 June 2013 15:31, Borislav Petkov <bp@...e.de> wrote:
>
>> Hold on, you say above "easily saturate minimum frequency and lead the
>> CPU to max". I read this as we jump straight to max P-state where we
>> even boost.
>
>Probably he meant: "At lowest levels of frequencies, a small load on system
>may look like a huge one. like: 20-30% load on max freq can be 95% load
>on min freq. And so we jump to max freq even for this load and return back
>pretty quickly as this load doesn't sustain for longer. over that we wait for
>load to go over up_threshold to increase freq."
>
>> "CPU to max" finishes the work faster than middle frequencies, if you're
>> CPU-bound.
>
>He isn't removing this feature at all.
>
>Current code is:
>
>if (load > up_threshold)
>   goto maxfreq.
>else
>   don't increase freq, maybe decrease it in steps
>
>What he is doing is:
>
>if (load > up_threshold)
>   goto maxfreq.
>else
>   increase/decrease freq based on current load.
>
>So, if up_threshold is 95 and load remains < 95, his patch will
>give significant improvement both power & performance wise.
>
>Else, it shouldn't decrease it.