From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39186) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WxHkL-0003O1-02 for qemu-devel@nongnu.org; Wed, 18 Jun 2014 11:26:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WxHkD-0008Kw-EH for qemu-devel@nongnu.org; Wed, 18 Jun 2014 11:25:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:4585) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WxHkD-0008Kp-3N for qemu-devel@nongnu.org; Wed, 18 Jun 2014 11:25:49 -0400 Date: Wed, 18 Jun 2014 18:26:05 +0300 From: "Michael S. Tsirkin" Message-ID: <20140618152605.GA11528@redhat.com> References: <20140613111703.22108.14322.stgit@bahia.local> <20140617073631.GL16768@stefanha-thinkpad.redhat.com> <539FF0E3.6040407@suse.de> <20140618103814.GG14030@stefanha-thinkpad.redhat.com> <20140618143521.3941fd4f@bahia.local> <20140618151249.GA1697@redhat.com> <53A1ACC9.2080305@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53A1ACC9.2080305@suse.de> Subject: Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: Kevin Wolf , Peter Maydell , Anthony Liguori , Juan Quintela , Stefan Hajnoczi , Rusty Russell , qemu-devel@nongnu.org, aneesh.kumar@linux.vnet.ibm.com, Stefan Hajnoczi , Amit Shah , Paolo Bonzini , Andreas =?iso-8859-1?Q?F=E4rber?= , Greg Kurz On Wed, Jun 18, 2014 at 05:14:17PM +0200, Alexander Graf wrote: > > On 18.06.14 17:12, Michael S. Tsirkin wrote: > >On Wed, Jun 18, 2014 at 02:35:21PM +0200, Greg Kurz wrote: > >>On Wed, 18 Jun 2014 18:38:14 +0800 > >>Stefan Hajnoczi wrote: > >> > >>>On Tue, Jun 17, 2014 at 09:40:19AM +0200, Alexander Graf wrote: > >>>>On 17.06.14 09:36, Stefan Hajnoczi wrote: > >>>>>On Fri, Jun 13, 2014 at 01:18:00PM +0200, Greg Kurz wrote: > >>>>>>This version merges the changes requested during the v7 review, remarks from > >>>>>>ppc64 dump support review (yes, we talked about virtio there) and the work on > >>>>>>virtio subsections migration. Also two new patches have been added: > >>>>>>- patch #1 is a preliminary fix for virtio-serial posted by Alexander Graf > >>>>>>- patch #9 prepares the work on the virtio_is_big_endian() helper > >>>>>> > >>>>>>The most significant changes are: > >>>>>>- introduction of a new CPU method for virtio > >>>>>>- endianness is taken from CPU that resets the device > >>>>>>- fastpath virtio memory accessors for fixed endian targets > >>>>>>- VMState based virtio subsections (compatibility friendly) > >>>>>I'm surprised it's not enough for the virtio device to have an > >>>>>endianness field (big/little). It seems these patches make endianness > >>>>>depend on the CPUState through which the device is being accessed. > >>>>> > >>>>>Can you explain why it's necessary to check the CPUState? > >>>>They only check CPUState at the point in time of reset, as that's the only > >>>>case where we can derive the implicit endian configuration from :). > >>>What bothers me is that real hardware can't do this. Given that VIRTIO > >>>1.0 is always little-endian I guess this is just a temporary hack for > >>>ppc little-endian. Would be nice to add a comment so it's clear why > >>>this approach is being taken instead of a cleaner solution. > >>> > >>>Stefan > >>Hi Stefan, > >> > >>Previous versions of this patch set had such comments: > >> > >>"virtio data structures are defined as "target endian", which assumes > >>that's a fixed value. In fact, that actually means it's platform-specific. > >>The OASIS virtio 1.0 spec will fix this, by making all little endian. > >> > >>We need to support both implementations and we want to share as much code > >>as possible." > >> > >>but these lines got lost between v6 and v7... my bad... :-\ > >> > >>I agree all of this is a hack but: > >>- it has been on the table for nearly a year > >>- ppc LE distros are already available > >>- the memory accessors part makes sense for 1.0 > >> > >>and, speaking of 1.0, I couldn't find any clue about when QEMU would support > >>this (Cc'ing Rusty for his input), but we (IBM and distro partners) need > >>ppc LE support now. > >> > >>Cheers. > >QEMU 2.2 I think. > > > >One disadvantage of this work is that it removes some of the stimulus > >for people to work on 1.0, replacing it with hacks. Hmm. > > If you prefer I can also apply these patches and send a pull request for > them. > > > Alex Not yet, please. v8 still got some comments, so we need to get v9. Then give people a bit of time to review. If everyone's happy it should be mergeable in about a week from now. Also there are Paolo's patches already in queue which will conflict, not sure it's a good time for you to step up and start merging virtio patches. I'm not nacking, chill :) I know you want these patches very much, but they aren't yet 100% ready anyway and I don't see why, meanwhile, I shouldn't mention the downsides for others to consider. -- MST