From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:36813) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R8f8G-0004sV-9l for qemu-devel@nongnu.org; Tue, 27 Sep 2011 17:24:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1R8f8F-0001aV-3p for qemu-devel@nongnu.org; Tue, 27 Sep 2011 17:24:04 -0400 Received: from mail-yx0-f173.google.com ([209.85.213.173]:38238) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R8f8F-0001aN-1E for qemu-devel@nongnu.org; Tue, 27 Sep 2011 17:24:03 -0400 Received: by yxl11 with SMTP id 11so7355073yxl.4 for ; Tue, 27 Sep 2011 14:24:02 -0700 (PDT) Message-ID: <4E823EEE.3030807@codemonkey.ws> Date: Tue, 27 Sep 2011 16:23:58 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <1317133583-25212-1-git-send-email-avi@redhat.com> <4E81EB8A.3070202@siemens.com> <4E81F43B.1040708@codemonkey.ws> <4E81FC29.9090503@redhat.com> In-Reply-To: <4E81FC29.9090503@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] event_notifier: move to top-level directory List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Kevin Wolf , Jan Kiszka , Stefan Hajnoczi , qemu-devel@nongnu.org, Avi Kivity On 09/27/2011 11:39 AM, Paolo Bonzini wrote: > On 09/27/2011 06:05 PM, Anthony Liguori wrote: >> Actually, for posix-aio, we can just switch to using g_idle_add(). >> g_idle_add() uses g_source_attach which is thread safe. g_idle_add() >> gives you a thread safe mechanism to defer a piece of work to the >> main loop which is really what we want here. > > For that, a bottom half would also do (apart that I am not sure it is > async-safe with TCG). In fact, that would make sense since all of > posix_aio_process_queue could become a bottom half. Bottom halves are signal safe, not thread safe. To make bottom halves thread safe, you would (in the very least) have to add some barriers when reading/writing the scheduling flag. I think it's much better to just use GIdle sources though. >> This can actually be made to work with sync I/O emulation too by >> having another GMainLoop in the sync I/O loop although I thought I >> recalled a patch series to remove that stuff. > > ... which stuff? :) The sync I/O emulation. Since sync I/O is done in block drivers, they can just use coroutine I/O instead of sync I/O. > Another GMainLoop in the sync I/O loop is problematic for > two reasons: 1) the sync I/O loop does not relinquish the I/O thread mutex, > which makes it very different from the outer loop; 2) a nested GMainLoop keeps > polling all the file descriptors in the outer loop, which requires you to cope > with reentrancy in those monitor commands that flush AIO. Re: (2), you can use a separate aio GMainContext. The trick is that you need to keep a global current main context that switches when you enter the AIO main loop. It's doable, but since I think we're on the verge of eliminating sync I/O emulation, that's probably a better path to pursue. Regards, Anthony Liguori > > Paolo >