From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v3 COLOPre 16/26] tools/libx{l, c}: add back channel to libxc Date: Wed, 1 Jul 2015 11:42:18 +0100 Message-ID: <1435747338.21469.252.camel@citrix.com> References: <1435213552-10556-1-git-send-email-yanghy@cn.fujitsu.com> <1435213552-10556-17-git-send-email-yanghy@cn.fujitsu.com> <1435659052.21469.68.camel@citrix.com> <559352B6.2010400@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <559352B6.2010400@cn.fujitsu.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Yang Hongyang Cc: wei.liu2@citrix.com, wency@cn.fujitsu.com, andrew.cooper3@citrix.com, yunhong.jiang@intel.com, eddie.dong@intel.com, xen-devel@lists.xen.org, guijianfeng@cn.fujitsu.com, rshriram@cs.ubc.ca, Ian Jackson List-Id: xen-devel@lists.xenproject.org On Wed, 2015-07-01 at 10:38 +0800, Yang Hongyang wrote: > > On 06/30/2015 06:10 PM, Ian Campbell wrote: > > On Thu, 2015-06-25 at 14:25 +0800, Yang Hongyang wrote: > >> We need to send secondary's dirty page pfns back to primary. > > > > In v2 Ian asked (<21888.2988.774072.32946@mariner.uk.xensource.com>): > > > > In the pdf > > http://www.socc2013.org/home/program/a3-dong.pdf?attredirects=0 > > linked from the wiki page > > http://wiki.xen.org/wiki/COLO_-_Coarse_Grain_Lock_Stepping > > it says that the secondary keeps a copy of the original contents of > > its dirty pages. So I don't understand why you need to send the dirty > > bitmap to the primary. > > > > Which I don't see an answer for in my archive. Have I missed (or > > misplaced) the answer? > > Sorry, seems that I misplaced the answer to: > [PATCH v2 COLOPre 09/13] tools/libxl: Update libxl_save_msgs_gen.pl to support > return data from xl to xc > > > Thanks for this. I would have some comments on the details, but first > > I want to properly understand your use case. So while I'm the author > > and maintainer of this save helper, I won't review this in detail just > > yet. I'm following the thread about what this is for... > > We need to send secondary's dirty page pfn back to primary. Primary will > then send pages that are both dirtied on primary/secondary to secondary. > in this way the secondary's memory will be consistent with primary. > > As we disscussed in [PATCH v2 COLOPre 04/13] tools/libxc: export xc_bitops.h > If we move this operation to libxc layer, this patch could be dropped. This doesn't seem to be a response to Ian's question which I quoted above. The crux of the question is that the design contained in those links does not appear to require a back channel, because it does not require a dirty bitmap to go from secondary to primary. Asserting a need to do so does not answer the question. Ian.