linux-kernel - RE: Performance drop on Baytrail with 4.5-rc2

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Date:	Wed, 3 Feb 2016 20:18:21 +0100 (CET)
From:	Thomas Voegtle <thomas@...gtle-clan.de>
To:	"Longepe, Philippe" <philippe.longepe@...el.com>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Gasparini, Stephane" <stephane.gasparini@...el.com>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
Subject: RE: Performance drop on Baytrail with 4.5-rc2

On Wed, 3 Feb 2016, Longepe, Philippe wrote:

> Thank you for sharing this test. I just did a quick test and yes this is 
> really interesting !
>
> Without the scale option, the load is close to 100% for each cpus (so 
> the pstates are increasing up to the turbo frequency) but with 
> scale=320:208, the load is oscillating (close to 50% in average), so the 
> requested frequencies are lower (the power is also reduced).
>
> I have a patch (not yet submitted) that reduce the gap for such a use case.

That's nice, glad the benchmark helped.

> As a temporary solution, you can also switch to performance with:
>
> sudo su
> echo performance > /sys/devices/system/cpu/cpu*/scaling_governor

Yes, ok, thanks.

> However, I still don't know why there is 50% of idle with the scale 
> option (is it using a Hw accelerator ?).


Mh. I don't know. I always thought this is stuff which is not that 
threadable as the mpeg to mp4 conversion, or something like that?


Thanks,

   Thomas