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

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Date:	Mon, 14 Sep 2009 11:30:10 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	John Stoffel <john@...ffel.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, lenb@...nel.org, mingo@...e.hu,
	akpm@...ux-foundation.org, peterz@...radead.org,
	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, 2009-09-11 at 15:16 -0400, John Stoffel 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 savings,
> Arjan> 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 algorithm
> Arjan> 1 disk		107 Mb/s	85 Mb/s		105 Mb/s
> Arjan> 2 disks		215 Mb/s	123 Mb/s	209 Mb/s
> Arjan> 12 disks	590 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,
We start fio and always ask it running for 15 minutes.

>  and b) how much (or average) power used for the
> duration of the test?  
The power consumption with the patch almost is equal to the one
without the patch. But the fio result is far better with the patch.

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

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