From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1LAt7e-00068T-59
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 16:31:02 -0500
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1LAt7c-000675-K5
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 16:31:01 -0500
Received: from [199.232.76.173] (port=36628 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1LAt7c-00066t-AA
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 16:31:00 -0500
Received: from verein.lst.de ([213.95.11.210]:34085)
	by monty-python.gnu.org with esmtps
	(TLS-1.0:DHE_RSA_3DES_EDE_CBC_SHA1:24) (Exim 4.60)
	(envelope-from <hch@lst.de>) id 1LAt7b-0002j9-M7
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 16:31:00 -0500
Date: Thu, 11 Dec 2008 22:30:55 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool
Message-ID: <20081211213055.GA2399@lst.de>
References: <493E941D.4000608@redhat.com> <493E965E.5050701@us.ibm.com>
	<20081210164401.GF18814@random.random>
	<493FFAB6.2000106@codemonkey.ws> <493FFC8E.9080802@redhat.com>
	<49400F69.8080707@codemonkey.ws>
	<20081210190810.GG18814@random.random>
	<20081211131222.GA14908@random.random>
	<494130B5.2080800@redhat.com>
	<20081211155335.GE14908@random.random>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20081211155335.GE14908@random.random>
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: Gerd Hoffmann <kraxel@redhat.com>, kvm-devel <kvm@vger.kernel.org>

On Thu, Dec 11, 2008 at 04:53:35PM +0100, Andrea Arcangeli wrote:
> >   * It can't handle block allocation.  Kernel handles that by doing
> >     such writes synchronously via VFS layer (instead of the separate
> >     aio code paths).  Leads to horrible performance and bug reports
> >     such as "installs on sparse files are very slow".
> 
> I think here you mean O_DIRECT regardless of aio/sync API, I doubt aio
> has any relevance to block allocation in any way, so whatever problem
> we have with kernel API and O_DIRECT should also be there with
> sync-api + userland threads and O_DIRECT.

userland threads with O_DIRECT means only the thread doing block
allocation gets stalled, not any other.