From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1KdmDv-0003CJ-9L
	for qemu-devel@nongnu.org; Thu, 11 Sep 2008 09:28:39 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1KdmDt-0003AH-Ba
	for qemu-devel@nongnu.org; Thu, 11 Sep 2008 09:28:38 -0400
Received: from [199.232.76.173] (port=34593 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1KdmDt-0003A6-4V
	for qemu-devel@nongnu.org; Thu, 11 Sep 2008 09:28:37 -0400
Received: from mail2.shareable.org ([80.68.89.115]:35090)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <jamie@shareable.org>) id 1KdmDs-0006Rp-Gc
	for qemu-devel@nongnu.org; Thu, 11 Sep 2008 09:28:36 -0400
Date: Thu, 11 Sep 2008 14:28:31 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] Re: [PATCH][RFC] Refactor AIO to allow multiple AIO
	implementations
Message-ID: <20080911132831.GD16427@shareable.org>
References: <1221061788-26166-1-git-send-email-aliguori@us.ibm.com>
	<48C8CD4E.1020705@redhat.com> <48C91302.70207@us.ibm.com>
	<48C91A00.3060403@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <48C91A00.3060403@redhat.com>
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org
Cc: Anthony Liguori <aliguori@us.ibm.com>, Ryan Harper <ryanh@us.ibm.com>, kvm@vger.kernel.org

Gerd Hoffmann wrote:
> > (I think the best
> > route is a thread-pool based implementation).
> 
> Not sure about that.  linux-aio would have the advantage that the kernel
> knows about all the requests in flight and probably can do a better job
> on I/O ordering and scheduling then.  But once we can have multiple
> different implementations we can just try ;)

Won't posix-aio give the same info to the kernel when used with a
sufficiently avante-garde Linux distro?

I'm under the impression that linux-aio is better in every way, as
I think Anthony Liguori posted a while back:

>>>  Threads are a poor substitute for a proper AIO interface.
>>>  linux-aio gives you everything you could possibly want in an
>>>  interface since it allows you to submit multiple vectored operations
>>>  in a single syscall, use an fd to signal request completion,
>>>  complete multiple requests in a single syscall, and inject barriers
>>>  via fdsync.

But knowing about request in flight, I/O ordering etc. seem equally
available via posix-aio on a distro where that calls linux-aio
(i.e. not the Glibc implementation).

-- Jamie