From: Ankit Jain <jankit@suse.de>
Subject: Re: [RFC][PATCH] Make io_submit non-blocking
Date: Thu, 26 Jul 2012 01:47:24 +0530
Message-ID: <50105454.5080400@suse.de>
References: <500E89D1.9010303@suse.de> <20120724223702.GB6723@lenny.home.zabbo.net>
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Cc: Al Viro <viro@zeniv.linux.org.uk>, bcrl@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
	linux-kernel@vger.kernel.org, Jan Kara <jack@suse.cz>
To: Zach Brown <zab@zabbo.net>
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In-Reply-To: <20120724223702.GB6723@lenny.home.zabbo.net>
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On 07/25/2012 04:07 AM, Zach Brown wrote:
> On Tue, Jul 24, 2012 at 05:11:05PM +0530, Ankit Jain wrote:
[snip]
>> With this patch, io_submit prepares all the kiocbs and then
>> adds (kicks) them to ctx->run_list (kicked) in one go and then
>> schedules the workqueue. The actual operations are not executed
>> on io_submit's process context, so it can return very quickly.
> 
> Strong nack; this isn't safe without having done the work to ensure that
> all the task_struct references under the f_op->aio_*() paths won't be
> horribly confused to find a kernel thread instead of the process that
> called io_submit().
> 
> The one-off handling of the submitters's cred is an indication that
> there might be other cases to worry about :).

Makes sense, I will try to look into this.

>> 3. Also, I tried not using aio_queue_work from io_submit call, and instead
>> depending on an already scheduled one or the iocbs being run when
>> io_getevents gets called. This seemed to give improved perfomance. But
>> does this constitute as change of api semantics?
> 
> You can't rely on io_getevents() being called for forward progress.  Its
> perfectly reasonable for a task to wait for io completion by polling an
> eventfd that aio_complete() notifies, for instance.

Ah okay, didn't realize that.

Thanks,
-- 
Ankit Jain
SUSE Labs


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