From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54441) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YnTD3-0007GS-CN for qemu-devel@nongnu.org; Wed, 29 Apr 2015 10:43:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YnTCu-0007JJ-Hs for qemu-devel@nongnu.org; Wed, 29 Apr 2015 10:43:33 -0400 Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:37562) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YnTCu-0007It-8T for qemu-devel@nongnu.org; Wed, 29 Apr 2015 10:43:24 -0400 Received: from /spool/local by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 29 Apr 2015 15:43:22 +0100 Received: from b06cxnps4074.portsmouth.uk.ibm.com (d06relay11.portsmouth.uk.ibm.com [9.149.109.196]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id E0A0B17D8042 for ; Wed, 29 Apr 2015 15:44:01 +0100 (BST) Received: from d06av07.portsmouth.uk.ibm.com (d06av07.portsmouth.uk.ibm.com [9.149.37.248]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t3TEhKYg56819924 for ; Wed, 29 Apr 2015 14:43:20 GMT Received: from d06av07.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av07.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t3TEhJLc020438 for ; Wed, 29 Apr 2015 10:43:20 -0400 Message-ID: <5540EE07.6020502@de.ibm.com> Date: Wed, 29 Apr 2015 16:43:19 +0200 From: Christian Borntraeger MIME-Version: 1.0 References: <1430221873-5788-1-git-send-email-shannon.zhao@linaro.org> <20150428151249-mutt-send-email-mst@redhat.com> <20150428152419.67bc77b1.cornelia.huck@de.ibm.com> <20150428160354-mutt-send-email-mst@redhat.com> <20150428201255-mutt-send-email-mst@redhat.com> <20150428203016-mutt-send-email-mst@redhat.com> <554093B3.2080205@de.ibm.com> <20150429105215.0a1122f2.cornelia.huck@de.ibm.com> <20150429103204.GA12976@redhat.com> In-Reply-To: <20150429103204.GA12976@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v4 0/2] virtio: Move host features to backends List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" , Cornelia Huck Cc: Peter Maydell , hangaohuai@huawei.com, "Huangpeng (Peter)" , QEMU Developers , Shannon Zhao , Shannon Zhao , Paolo Bonzini , Christoffer Dall Am 29.04.2015 um 12:32 schrieb Michael S. Tsirkin: > On Wed, Apr 29, 2015 at 10:52:15AM +0200, Cornelia Huck wrote: >> On Wed, 29 Apr 2015 10:17:55 +0200 >> Christian Borntraeger wrote: >> >>> Am 28.04.2015 um 20:32 schrieb Michael S. Tsirkin: >>>> On Tue, Apr 28, 2015 at 08:14:44PM +0200, Michael S. Tsirkin wrote: >>>>> On Tue, Apr 28, 2015 at 04:35:16PM +0200, Michael S. Tsirkin wrote: >>>>>> On Tue, Apr 28, 2015 at 03:24:19PM +0200, Cornelia Huck wrote: >>>>>>> On Tue, 28 Apr 2015 14:16:40 +0100 >>>>>>> Peter Maydell wrote: >>>>>>> >>>>>>>> On 28 April 2015 at 14:13, Michael S. Tsirkin wrote: >>>>>>>>> The patches look correct to me too, but I want s390 >>>>>>>>> cleaned up so it does not include COMMON_FEATURES >>>>>>>>> in 100 places, and I prefer merging it all together. >>>>>>>> >>>>>>>> It seems a bit harsh to ask Shannon to do s390 cleanup when >>>>>>>> he doesn't have any access to s390 guests or test cases... >>>>>>>> Making S390 put COMMON_FEATURES in the right places seems >>>>>>>> to me like a separate bit of s390-specific cleanup. >>>>>>> >>>>>>> Yep, see my other reply... I'm not quite sure what's wrong with >>>>>>> event_idx on virtio-blk for s390-virtio, or I would gladly make this >>>>>>> consistent with the other transports. Any hints appreciated :) >>>>>> >>>>>> Is this still happening? >>>>>> >>>>>> It is possible that what was missing was >>>>>> 92045d80badc43c9f95897aad675dc7ef17a3b3f >>>>>> and/or >>>>>> a281ebc11a6917fbc27e1a93bb5772cd14e241fc >>>>>> >>>>> >>>>> Found this: >>>>> http://thread.gmane.org/gmane.comp.emulators.qemu/280334/focus=280357 >>>>> so it's unlikely: these commits are from 2012, you saw >>>>> issues in 2014. >>>>> >>>>> We really need to fix it. virtio 1 work will be much easier if >>>>> we can just move features into virtio dev. >>> >>> Yes, we have to understand why event_idx breaks for the s390-virtio transport. >>>> >>>> I'm beginning to suspect this is a wrong implementation of barriers. >>>> Questions: >>>> - which compiler to you use? >>>> - can you pls disassemble code for smp_wmb smp_rmb and smp_mb? >>>> They all must do br %r14 I think, and this is what >>>> s390x-linux-gnu-gcc generated for me: >>>> s390x-linux-gnu-gcc (GCC) 4.9.1 >>> >>> s390 has strong memory ordering. Reads are in order, writes are in order. >>> bcr 14,0 or bcr 15,0 then only serialize the reads against the writes. >>> So smp_rmb and smp_wmb can be implemented as no-ops like QEMU. >>> If your change "fixes" the issue then we have a problem somewhere else >> >> And (surprise, surprise) virtio-blk now works - but it also works when >> I back out the atomic.h change again. No barrier problems :) >> >> Good news is that we can change s390-virtio to be just like the other >> transports. Although I'd like to understand why it was broken before. >> Maybe a guest change? > > Or a compiler change? Try compiling some old release, see what happens. > Anyway, let's move DEFINE_VIRTIO_COMMON_FEATURES into the base class > now. Can you send a patch pls? 3.17 as guest fails, 3.18 as guest works. Not sure yet why.