linux-kernel - Re: PATCH] cpuidle: A new variant of the menu governor to boost IO performance

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Date:	Fri, 11 Sep 2009 21:51:31 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	"John Stoffel" <john@...ffel.org>
Cc:	linux-kernel@...r.kernel.org, lenb@...nel.org, mingo@...e.hu,
	akpm@...ux-foundation.org, peterz@...radead.org,
	yanmin_zhang@...ux.intel.com, torvalds@...ux-foundation.org,
	jens.axboe@...cle.com
Subject: Re: PATCH] cpuidle: A new variant of the menu governor to boost IO
 performance

On Fri, 11 Sep 2009 15:16:49 -0400
"John Stoffel" <john@...ffel.org> wrote:

> >>>>> "Arjan" == Arjan van de Ven <arjan@...radead.org> writes:
> 
> Arjan> From: Arjan van de Ven <arjan@...ux.intel.com>
> Arjan> Subject: [PATCH] cpuidle: A new variant of the menu governor
> 
> Arjan> This patch adds a new idle governor which balances power
> Arjan> savings, energy efficiency and performance impact.
> 
> Arjan> The reason for a reworked governor is that there have been
> Arjan> serious performance issues reported with the existing code
> Arjan> on Nehalem server systems.
> 
> Arjan> To show this I'm sure Andrew wants to see benchmark results:
> Arjan> (benchmark is "fio", "no cstates" is using "idle=poll")
> 
> Arjan> 		no cstates	current linux	new
> Arjan> algorithm 1 disk		107 Mb/s	85
> Arjan> Mb/s		105 Mb/s 2 disks		215
> Arjan> Mb/s	123 Mb/s	209 Mb/s 12 disks	590
> Arjan> Mb/s	320 Mb/s	585 Mb/s
> 
> Don't you need another row or three where you show a) how much time
> each test took, and b) how much (or average) power used for the
> duration of the test?  
> 
> I'm just curious if the new algorithm (or even the current one!) saves
> any appreciable power over the 'no cstates' case.  It's not clear what
> the savings are.  

if you don't do C states your cpu is likely using 50 Watts more power.
not an option in general.

> 
> Also, latency in terms of switching to higher power and then back down
> would be nice to see.

these are C states not P states.


latency depends on the cpu; this is exposed in sysfs;
tends to be for the deepest C state in the 80 to 200 usec range.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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