From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH] [RFC] Building guests on monotonic Xen system time Date: Sat, 24 May 2008 08:34:17 +0100 Message-ID: References: <20080523164452796.00000001192@djm-pc> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080523164452796.00000001192@djm-pc> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: "dan.magenheimer@oracle.com" , "Xen-Devel (E-mail)" Cc: Dave Winchell List-Id: xen-devel@lists.xenproject.org On 23/5/08 23:44, "Dan Magenheimer" wrote: > Here's another option: I think delay_for_missed_ticks is > the only mode where time must be set backwards. All of the > other modes track wallclock. It looks possible that we > could enforce monotonicity for the other three modes and > not enforce it for delay_for_missed_ticks (which is, > unfortunately, the default). > > If this is acceptable to you (and you don't disagree with > my "only mode...set backwards" conjecture), I'll try to > code a patch for this. I agree with your analysis. I couldn't remember if any modes other than 0 would require non-monotonic time across VCPUs, but it does appear that this property is exclusive to mode 0. > P.S. I think the answer is no, but is there any way to specify > gang-scheduling for a domain? If so, we could say if your > OS is non-resilient to preemption and your application requires > time monotonicity, you must specify gang scheduling. There isn't currently a way to request gang scheduling. I think that is a second step anyway. It sounds like you could simply turn off your monotonicity checks for timer mode 0 and I'll be happy. I have a pretty clear vision of what I want now, so I will make the necessary adjustments to the patch. Then we can go from there if you think further modifications are required. -- Keir