linux-kernel - Re: Approaches to making io

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Message-ID: <4E5F690C.4010209@akkadia.org>
Date:	Thu, 01 Sep 2011 07:14:20 -0400
From:	Ulrich Drepper <drepper@...adia.org>
To:	Jeremy Allison <jra@...ba.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Ehrenberg <dehrenberg@...gle.com>,
	Jens Axboe <axboe@...nel.dk>, Jeff Moyer <jmoyer@...hat.com>,
	linux-kernel@...r.kernel.org, linux-aio@...ck.org
Subject: Re: Approaches to making io_submit not block

On 08/31/2011 12:59 PM, Jeremy Allison wrote:
> I get that, but isn't that what the aio_init(const struct aioinit *init) call is meant to
> solve ?

The problem cannot be solved by something that trivial.  Any thread can
be delayed indefinitely.  If this happens for a file descriptor chances
are that all threads for the same file descriptor are affected while
there is I/O for all the other file descriptors ready to run.  I don't
say this is anywhere near optimal or even good, at least it doesn't
amplify problems.  If you know you want more parallelism on the same
file descriptor, dup it.  If you don't want anyone like me implementing
stupid limitations finally fix the kernel aio interface so that it is
usable.

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