From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: common time reference between domU and dom0 Date: Fri, 10 Dec 2010 10:45:08 +0000 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: James Harper , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 10/12/2010 10:20, "James Harper" wrote: >> On 10/12/2010 08:23, "James Harper" > wrote: >> >>>> >>>> System time, as exposed to guests by Xen, should be good enough. >>>> >>> >>> How is this exposed for HVM systems? >> >> Given all HVM guest time sources are trapped to the hypervisor, > including >> TSC, you may as well just use the HVMOP_get_time hypercall. >> > > Is that a new call? I don't see it mentioned in 4.0-testing anywhere. Yeah I think it's in 4.1 only. > Is there a fallback if HVMOP_get_time doesn't exist? Switch on vtsc (might be default) and just use RDTSC? Might be good enough. I'm not sure that computing system time yourself from fields in shared info works well for HVM guests. HVMOP_get_time I think had been in XenServer patch queue a while and has just been pulled across to upstream. -- Keir > James >