From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH 0/4] HVM Virtual S3 Date: Thu, 17 May 2007 08:41:11 +0100 Message-ID: References: <1104166E0B63A341805FDB977862AAD23BC8FF@pdsmsx414.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1104166E0B63A341805FDB977862AAD23BC8FF@pdsmsx414.ccr.corp.intel.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: "Yu, Ke" , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 17/5/07 03:32, "Yu, Ke" wrote: > My concern here is that: save/restore is a heavy operation just like S4 > (hibernate), while the purpose of S3 is quick suspend and quick resume > comapred to S4. if we implement S3 like save/restore, I don't see the value > here, because HVM save/resotre or HVM S4 is just enough. How do you think? I do not think that pure virtual S3 by itself makes sense. Unless the whole machine is going into S3, what really is the difference between a HVM guest in S3 and an HVM guest that simply is idle and so has all its VCPUs HLTed 99.9% of the time? Both are tying up memory resource, neither is burning significant CPU resource or I/O resource. Virtual S3 *does* make sense with HVM save/restore because it makes even an HVM guest without PV drivers aware of the save/restore event so it can do things like resync its clock. That is why we are interested in virtual S3: only as an adjunct to save/restore. Another application would be as part of host S3. Given that those patches currently save/restore all domains (which actually I think is stupid, but that's for a separate email) you should automatically improve host S3 by integrating with save/restore. However, again, the benefit is not the effects of the state the guest finds itself in --- since S3 is not enormously meaningful in a virtualised environment --- but because of the side effects we enjoy when the guest awakens and resyncs its world. -- Keir