From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1JtnRB-0004Pr-8N for qemu-devel@nongnu.org; Wed, 07 May 2008 13:28:17 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1JtnRA-0004Op-EA for qemu-devel@nongnu.org; Wed, 07 May 2008 13:28:16 -0400 Received: from [199.232.76.173] (port=44350 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1JtnRA-0004Oc-1B for qemu-devel@nongnu.org; Wed, 07 May 2008 13:28:16 -0400 Received: from ns2.suse.de ([195.135.220.15] helo=mx2.suse.de) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1JtnR9-00069d-ME for qemu-devel@nongnu.org; Wed, 07 May 2008 13:28:16 -0400 Message-ID: <4821E596.1050306@suse.de> Date: Wed, 07 May 2008 19:23:34 +0200 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [4367] Align file accesses with cache=off (Kevin Wolf, Laurent Vivier) References: <4820D905.4020407@bellard.org> <48216579.3060204@suse.de> <20080507123733.GA2822@shareable.org> <4821A8F0.9070506@suse.de> <20080507162642.GA7324@shareable.org> In-Reply-To: <20080507162642.GA7324@shareable.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: jamie@shareable.org Cc: qemu-devel@nongnu.org Jamie Lokier schrieb: > Kevin Wolf wrote: >> No, nobody mentioned the recursion problem. > > Hmm. I concede you're right in the sense that it was mentioned, but > on a different thread about QEMU AIO recently :-) Hm, okay. Will read that thread if I can find it. But I hope the recursion thing is fixed now anyway. > Following the paragraph about two file descriptors, there was: > >>> I'm not sure if that works, though. On some OSes, if a file has any >>> non-O_DIRECT open descriptor, all I/O is buffered ignoring the >>> O_DIRECT flag. If both are allowed simultaneously, I'm not sure what >>> happens with cache-coherency between direct I/Os and buffered I/Os. > > Not sure if that is quite the same thing :-) Am I completely mistaken or is this still about two (or more) different file descriptors where one of them is non-O_DIRECT? > I did miss that switching O_DIRECT on/off while AIOs are in flight on > that descriptor might be dodgy (implementation dependent), and that it > might not do the right things w.r.t. cohrency. Me too. I just was too confident that it actually works when Laurent says it was better. You know, for every problem there is an answer that is clear, simple and wrong. ;-) >> But even if so, this is more of a general feeling about how patches are >> handled and not only related to this patch. > > I agree and have a similar feeling, though it's not a bad thing > provided the issues are actually noticed, which they do seem to be. Actually, I do think it's a bad thing. Obviously, issues are noticed when the patch goes in and can be fixed then. Right. But what about the other 90% of the patches which don't get no attention at all? Nobody comments on them, they aren't committed, and after all they are wasted efforts. It's a bad thing because it slows down qemu development by (passively) rejecting patches which are fine or could be fixed easily. Kevin