linux-kernel - Re: [RFC] Block IO Controller V2

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Date:	Tue, 17 Nov 2009 11:45:00 -0500
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: [RFC] Block IO Controller V2 - some results

On Tue, 2009-11-17 at 17:17 +0100, Corrado Zoccolo wrote:
> Hi Vivek,
> the performance drop reported by Alan was my main concern about your
> approach. Probably you should mention/document somewhere that when the
> number of groups is too large, there is large decrease in random read
> performance.
> 
> However, we can check few things:
> * is this kernel built with HZ < 1000? The smallest idle CFQ will do
> is given by 2/HZ, so running with a small HZ will increase the impact
> of idling.

FYI:

CONFIG_NO_HZ=y
CONFIG_HZ_1000=y
CONFIG_HZ=1000



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