linux-kernel - Re: Linux disk performance.

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Message-ID: <458788D7.2070107@yahoo.com.au>
Date:	Tue, 19 Dec 2006 17:38:15 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Manish Regmi <regmi.manish@...il.com>
CC:	Erik Mouw <mouw@...linux.org>, kernelnewbies@...linux.org,
	linux-kernel@...r.kernel.org
Subject: Re: Linux disk performance.

Manish Regmi wrote:

> Nick Piggin:
> 
>> but
>> they look like they might be a (HZ quantised) delay coming from
>> block layer plugging.
> 
> 
> Sorry i didn´t understand what you mean.

When you submit a request to an empty block device queue, it can
get "plugged" for a number of timer ticks before any IO is actually
started. This is done for efficiency reasons and is independent of
the IO scheduler used.

Use the noop IO scheduler, as well as the attached patch, and let's
see what your numbers look like.

Thanks,
Nick

-- 
SUSE Labs, Novell Inc.

View attachment "block-no-plug.patch" of type "text/plain" (517 bytes)