From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LB3J8-00076p-UV for qemu-devel@nongnu.org; Fri, 12 Dec 2008 03:23:34 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LB3J7-00076V-RS for qemu-devel@nongnu.org; Fri, 12 Dec 2008 03:23:34 -0500 Received: from [199.232.76.173] (port=48811 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LB3J7-00076S-M1 for qemu-devel@nongnu.org; Fri, 12 Dec 2008 03:23:33 -0500 Received: from brick.kernel.dk ([93.163.65.50]:29478 helo=kernel.dk) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1LB3J7-0007jh-6G for qemu-devel@nongnu.org; Fri, 12 Dec 2008 03:23:33 -0500 Date: Fri, 12 Dec 2008 09:23:10 +0100 From: Jens Axboe Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool Message-ID: <20081212082309.GI23742@kernel.dk> References: <493FFC8E.9080802@redhat.com> <49400F69.8080707@codemonkey.ws> <20081210190810.GG18814@random.random> <20081211131222.GA14908@random.random> <494130B5.2080800@redhat.com> <20081211155335.GE14908@random.random> <49413B9C.3030703@redhat.com> <20081211164947.GD6809@random.random> <49414BC9.5090905@redhat.com> <20081211181116.GE6809@random.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081211181116.GE6809@random.random> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: aarcange@redhat.com, Gerd Hoffmann , kvm-devel On Thu, Dec 11 2008, Andrea Arcangeli wrote: > On Thu, Dec 11, 2008 at 06:20:09PM +0100, Gerd Hoffmann wrote: > > Andrea Arcangeli wrote: > > > On Thu, Dec 11, 2008 at 05:11:08PM +0100, Gerd Hoffmann wrote: > > >> Yes. But kernel aio requires O_DIRECT, so aio users are affected > > >> nevertheless. > > > > > > Are you sure? It surely wasn't the case... > > > > Tons of docs say so, but might be they are wrong, I didn't check. > > I guess those tons of docs are just wrong then ;). I see no mention of > O_DIRECT in `man io_submit` at least... I seem to recall initially aio > only worked without O_DIRECT... ;). It's quite the opposite, O_DIRECT > works best with kernel aio, not the other way around. O_DIRECT > read/writes look very much like non-O_DIRECT seeking reads. For > seeking sync-reads kernel aio pays off as well as with O_DIRECT. aio is only async with O_DIRECT, with buffered IO it's sync. -- Jens Axboe