linux-kernel - linux io_submit syscall duration

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Date:	Wed, 15 Nov 2006 09:39:14 +0200
From:	"Raz Ben-Jehuda(caro)" <raziebe@...il.com>
To:	linux-aio@...ck.org, "Linux Kernel" <linux-kernel@...r.kernel.org>
Cc:	bcrl@...ck.org, zach.brown@...cle.com
Subject: linux io_submit syscall duration

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 ?

would appreciate your help.
thank you

raz
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