From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:36303) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TRJMc-0004jr-Da for qemu-devel@nongnu.org; Thu, 25 Oct 2012 05:04:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TRJMR-0001sT-2r for qemu-devel@nongnu.org; Thu, 25 Oct 2012 05:04:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38267) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TRJMQ-0001sG-PO for qemu-devel@nongnu.org; Thu, 25 Oct 2012 05:04:19 -0400 Message-ID: <50890087.1080706@redhat.com> Date: Thu, 25 Oct 2012 11:04:07 +0200 From: Avi Kivity MIME-Version: 1.0 References: <1350897839-29593-1-git-send-email-pingfank@linux.vnet.ibm.com> <1350897839-29593-14-git-send-email-pingfank@linux.vnet.ibm.com> <50852299.8090109@redhat.com> <50865E3F.4010809@siemens.com> <5086656A.6060603@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [patch v4 13/16] e1000: add busy flag to anti broken device state List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Liu Ping Fan , Jan Kiszka , Marcelo Tosatti , "qemu-devel@nongnu.org" , liu ping fan , Anthony Liguori , Stefan Hajnoczi , Paolo Bonzini On 10/25/2012 11:00 AM, Peter Maydell wrote: > On 23 October 2012 10:37, Avi Kivity wrote: >> On 10/23/2012 11:32 AM, liu ping fan wrote: >>> On Tue, Oct 23, 2012 at 5:07 PM, Jan Kiszka wrote: >>>> On 2012-10-23 07:52, liu ping fan wrote: >>>>> On Mon, Oct 22, 2012 at 6:40 PM, Avi Kivity wrote: >>>>>> On 10/22/2012 11:23 AM, Liu Ping Fan wrote: >>>>> It will only record and fix the issue on one thread. But guest can >>>>> touch the emulated device on muti-threads. >>>> >>>> Sorry, what does that mean? A second VCPU accessing the device will >>>> simply be ignored when it races with another VCPU? Specifically >>>> >>> Yes, just ignored. For device which support many logic in parallel, >>> it should use independent busy flag for each logic >> >> We don't actually know that e1000 doesn't. Why won't writing into >> different registers in parallel work? > > Unless the device we're emulating supports multiple in > parallel accesses (and I bet 99.9% of the devices we model > don't) then the memory framework needs to serialise the > loads/stores. Otherwise it's just going to be excessively > hard to write a reliable device model. That's why we have a per-device lock. The busy flag breaks that model by discarding accesses that occur in parallel. -- error compiling committee.c: too many arguments to function