linux-kernel - Re: howto boost write(2) performance?

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Message-ID: <470BA14C.90608@panasas.com>
Date:	Tue, 09 Oct 2007 17:42:04 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Michael Stiller <ms@...ale.net>, linux-kernel@...r.kernel.org
Subject: Re: howto boost write(2) performance?

On Tue, Oct 09 2007 at 16:56 +0200, Andi Kleen <andi@...stfloor.org> wrote:
> Michael Stiller <ms@...ale.net> writes:
>> The write(2) performance is not good enough, the writer threads take to
>> much time, and i ask you for ideas, howto to boost the write
>> performance. 
> 
> You could use an O_DIRECT write if the data is suitably aligned
> and your IO sizes are big enough (O_DIRECT is usually a loss
> on small IOs). It will also be synchronous, but if you do it 
> from a separate thread anyways that should be fine.
> 
> -Andi

If your target is a SCSI target you can gain up to 15% by using
sg. Search on the net for the "sg utils" package. The source code
of sg_dd and others are a grate example of how to do it.

Other wise O_DIRECT is your friend. Also look for asynchronous
I/O so you have a few pending IO buffers to keep the pipes full.

Boaz

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