linux-kernel - RE: [PATCH] CPUIdle: Reevaluate C-states under CPU load to favor deeper C-states

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Message-ID: <37CAE120BAE10B42A790DD1418C8021D0136C7@DNCE02.ent.ti.com>
Date:	Wed, 9 Nov 2011 18:06:41 +0000
From:	"Chalhoub, Nicole" <n-chalhoub@...com>
To:	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>,
	"Hilman, Kevin" <khilman@...com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>
Subject: RE: [PATCH] CPUIdle: Reevaluate C-states under CPU load to favor
 deeper C-states

Hi Deepthi,

>
Texas Instruments France SA, 821 Avenue Jack Kilby, 06270 Villeneuve Loubet. 036 420 040 R.C.S Antibes. Capital de EUR 753.920

-----Original Message-----
> From: Deepthi Dharwar [mailto:deepthi@...ux.vnet.ibm.com]
> Sent: Wednesday, November 09, 2011 12:13 PM
> To: Hilman, Kevin
> Cc: linux-kernel@...r.kernel.org; Arjan van de Ven; linux-arm-
> kernel@...ts.infradead.org; linux-omap@...r.kernel.org; linux-
> pm@...ts.linux-foundation.org; Chalhoub, Nicole
> Subject: Re: [PATCH] CPUIdle: Reevaluate C-states under CPU load to favor
> deeper C-states

[...]
> By setting timers when we enter non-deepest C-state possible, such that
> when it fires we
> can re-evaluate and try moving into deeper and deeper C-states enhancing
> the
> power savings is a good feature to have.
>
> Looking at the current implementation, is it possible to have it as
> configurable option
> where one can enable/disable this functionality through the backhand
> driver ?

The timeout values of the c state timers are set in the backhand driver.
By setting the timeout to 0 the timers will not fire so you'll not have this functionality enabled

> Also I am thinking, instead of having them in governor
> wouldnt it be a good idea to have it implemented in
> the backhand driver itself ?
> --Deepthi


In fact each C-state had its own configurable timer, so it is a parameter characterizing a C-state as it is for the exit_latency and target_residency parameters.
And we wanted the timer to fire only when we do not go in deep Cstate due to a high load. This decision is made in the CPU idle governor. So the functionality should be seen from the governor..

Thanks and Regards
Nicole


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