From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NSFXP-0003gd-9b for qemu-devel@nongnu.org; Tue, 05 Jan 2010 14:57:55 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NSFXI-0003aG-6R for qemu-devel@nongnu.org; Tue, 05 Jan 2010 14:57:51 -0500 Received: from [199.232.76.173] (port=43273 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NSFXG-0003Zo-Lz for qemu-devel@nongnu.org; Tue, 05 Jan 2010 14:57:46 -0500 Received: from mx20.gnu.org ([199.232.41.8]:36417) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1NSFXG-0005Cg-33 for qemu-devel@nongnu.org; Tue, 05 Jan 2010 14:57:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NRtA0-0005Ph-UF for qemu-devel@nongnu.org; Mon, 04 Jan 2010 15:04:17 -0500 Date: Mon, 4 Jan 2010 22:01:16 +0200 From: "Michael S. Tsirkin" Message-ID: <20100104200116.GB21311@redhat.com> References: <1261382970-23251-1-git-send-email-pbonzini@redhat.com> <1261382970-23251-12-git-send-email-pbonzini@redhat.com> <4B424E95.4040806@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B424E95.4040806@codemonkey.ws> Subject: [Qemu-devel] Re: [PATCH 11/19] use a bottom half to run timers List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Paolo Bonzini , qemu-devel@nongnu.org On Mon, Jan 04, 2010 at 02:24:53PM -0600, Anthony Liguori wrote: > On 12/21/2009 02:09 AM, Paolo Bonzini wrote: >> Make the timer subsystem register its own bottom half instead of >> placing the bottom half code in the heart of the main loop. To >> test if an alarm timer is pending, just check if the bottom half is >> scheduled. >> >> Signed-off-by: Paolo Bonzini > > I'm not a huge fan of this for a couple reasons. The first is that it > introduces a subtle semantic change. Previously, timers always ran > before bottom halves whereas after this change, timers may run after > some bottoms halves but before others. While this should be okay in > principle, in practice, I'm sure it'll introduce regressions. I'd be > very surprised if cris wasn't affected by this. > > But more importantly, I think timer dispatch needs to be part of the > select loop. malc has a git tree that replaces host alarm timers with > select() timeouts. Where is that tree? IMO we need that, I am not sure all code is as signal-safe as it should be. At least crashes that I saw with winxp install seem to be related to signal handling. > This has a lot of really nice properties like it > eliminates the need for signals and EINTR handling. A move like this > would likely make this more difficult. > > I think the opposite sort of move makes more sense. Treating bottom > halves as 0-duration timer events. Unfortunately, things like cris do > not handle this sort of change very well. > > Regards, > > Anthony Liguori >