linux-kernel - Re: linux io_submit syscall duration

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Date:	Wed, 15 Nov 2006 08:47:21 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Raz Ben-Jehuda(caro)" <raziebe@...il.com>
Cc:	linux-aio@...ck.org, Linux Kernel <linux-kernel@...r.kernel.org>,
	bcrl@...ck.org, zach.brown@...cle.com
Subject: Re: linux io_submit syscall duration

On Wed, Nov 15 2006, Raz Ben-Jehuda(caro) wrote:
> Bnejamin hello.
> 
> My name is raz and i have encountered a problem with  io_submit.
> The maximum duration of a single io_submit operation when
> heavily stressing the system with large number of big (1MB) ios,
> reaches several hundereds ms.
> 
> I have been profiling it and it seems that the problem is the
> file->f_op->aio_read operation,
> a call that is made in fs/aio.c when coming from:
> sys_io_submit -->
>   io_submit_one -->
> 	  aio_run_iocb -->
>   		 *retry
> 
> 
> The test is initiating several hundered 1MB IOs over a single block device.
> 
> I understand that the assumption made was aio_read is asynchronous and no
> delay will occure, but isn't possible to do it in the workqueue context ?

This was discussed no more than a week ago on this list, please search the
archives for the thread.

-- 
Jens Axboe

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