From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool Date: Fri, 12 Dec 2008 09:23:10 +0100 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 Cc: Gerd Hoffmann , kvm-devel , aarcange@redhat.com To: qemu-devel@nongnu.org Return-path: Received: from brick.kernel.dk ([93.163.65.50]:24975 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750795AbYLLIX3 (ORCPT ); Fri, 12 Dec 2008 03:23:29 -0500 Content-Disposition: inline In-Reply-To: <20081211181116.GE6809@random.random> Sender: kvm-owner@vger.kernel.org List-ID: 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