From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:53861) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S9vm9-0006Bf-JC for qemu-devel@nongnu.org; Tue, 20 Mar 2012 05:54:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1S9vm3-0005N6-I1 for qemu-devel@nongnu.org; Tue, 20 Mar 2012 05:54:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51019) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S9vm3-0005Mm-Ao for qemu-devel@nongnu.org; Tue, 20 Mar 2012 05:54:39 -0400 Message-ID: <4F6854B2.8000209@redhat.com> Date: Tue, 20 Mar 2012 10:58:10 +0100 From: Kevin Wolf MIME-Version: 1.0 References: <1331603611-9103-1-git-send-email-zwu.kernel@gmail.com> <4F685230.9040209@redhat.com> In-Reply-To: <4F685230.9040209@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Zhi Yong Wu , Zhi Yong Wu , qemu-devel@nongnu.org, stefanha@linux.vnet.ibm.com Am 20.03.2012 10:47, schrieb Paolo Bonzini: > Il 20/03/2012 10:40, Zhi Yong Wu ha scritto: >> HI, Kevin, >> >> We hope that I/O throttling can be shipped without known issue in QEMU >> 1.1, so if you are available, can you give this patch some love? > > I'm sorry to say this, but I think I/O throttling is impossible to save. > As it is implemented now, it just cannot work in the presence of > synchronous I/O, except at the cost of busy waiting with the global > mutex taken. See the message from Stefan yesterday. qemu_aio_flush() is busy waiting with the global mutex taken anyway, so it doesn't change that much. Kevin