From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60358) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V3jI8-0000GL-Bk for qemu-devel@nongnu.org; Mon, 29 Jul 2013 04:59:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V3jI3-0006xt-J7 for qemu-devel@nongnu.org; Mon, 29 Jul 2013 04:58:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55047) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V3jI3-0006xS-Az for qemu-devel@nongnu.org; Mon, 29 Jul 2013 04:58:51 -0400 Date: Mon, 29 Jul 2013 10:58:40 +0200 From: Kevin Wolf Message-ID: <20130729085840.GC3721@dhcp-200-207.str.redhat.com> References: <1374396185-10870-1-git-send-email-pingfank@linux.vnet.ibm.com> <20130725120530.GJ21033@stefanha-thinkpad.redhat.com> <51F11AFB.9040008@siemens.com> <1A5D30F9703985AD026648F0@nimrod.local> <20130726084345.GE31438@stefanha-thinkpad.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130726084345.GE31438@stefanha-thinkpad.redhat.com> Subject: Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Stefan Hajnoczi , Alex Bligh , Jan Kiszka , Liu Ping Fan , qemu-devel@nongnu.org, Anthony Liguori , Paolo Bonzini Am 26.07.2013 um 10:43 hat Stefan Hajnoczi geschrieben: > On Thu, Jul 25, 2013 at 07:53:33PM +0100, Alex Bligh wrote: > > > > > > --On 25 July 2013 14:32:59 +0200 Jan Kiszka wrote: > > > > >>I would happily at a QEMUClock of each type to AioContext. They are after > > >>all pretty lightweight. > > > > > >What's the point of adding tones of QEMUClock instances? Considering > > >proper abstraction, how are they different for each AioContext? Will > > >they run against different clock sources, start/stop at different times? > > >If the answer is "they have different timer list", then fix this > > >incorrect abstraction. > > > > Even if I fix the abstraction, there is a question of whether it is > > necessary to have more than one timer list per AioContext, because > > the timer list is fundamentally per clock-source. I am currently > > just using QEMU_CLOCK_REALTIME as that's what the block drivers normally > > want. Will block drivers ever want timers from a different clock source? > > block.c and block/qed.c use vm_clock because block drivers should not do > guest I/O while the vm is stopped. This is especially true during live > migration where it's important to hand off the image file from the > source host to the destination host with good cache consistency. The > source host is not allowed to modify the image file anymore once the > destination host has resumed the guest. > > Block jobs use rt_clock because they aren't considered guest I/O. But considering your first paragraph, why is it safe to let block jobs running while we're migrating? Do we really do that? It sounds unsafe to me. Kevin