From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Winchell Subject: Re: [PATCH] Deferrable Timer Date: Thu, 17 Jul 2008 10:14:41 -0400 Message-ID: <487F53D1.6030104@virtualiron.com> References: <1104166E0B63A341805FDB977862AAD201BC154A@pdsmsx414.ccr.corp.intel.com> <1104166E0B63A341805FDB977862AAD201BF479B@pdsmsx414.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1104166E0B63A341805FDB977862AAD201BF479B@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" Cc: "Tian, Kevin" , xen-devel@lists.xensource.com, Dave Winchell , Keir Fraser , "Wei, Gang" List-Id: xen-devel@lists.xenproject.org Yu, Ke wrote: >Keir Fraser wrote: > > >>On 17/7/08 13:54, "Yu, Ke" wrote: >> >> >> >>>This patch adds new ac timer API set_timer_deferrable for the >>>deferrable timer. >>> >>> >>Whether this is worthwhile depends on what likely users there are. >>platform-timer overflow is not very compelling since if you're using >>anything other than PIT (which ought to be likely on a modern system >>supporting deep sleep) the overflow period should be multiple seconds. >> >> -- Keir >> >> > >True. Another user is the Px state sampling timer, which is 20ms. Other >potential timers (e.g. sched timer, hvm pt timers) are also under >evaluation, the principle is to make sure there is no performance >downgrade. > > Ke, One would think that hpet or vpt support for the guest-handles-missed-ticks policy would be a good application for a deferrable timer. If a deferrable timer were used, then the comparator (cmp) would have to be warped to a non-integer multiple of the period. This is because Linux reads the comparator register to estimate the delay since the interrupt was posted. I don't think warping like this will be a problem. At some point, I can test this. I think we could use the deferrable timer for the guest-does-not-handle-missed-ticks policy as well. Any investigation that you want to do in the platform timer area would be fine. Or I can do it, but that will probably be after I do the vpt.c/hpet.c integration work. thanks, Dave >Best Regards >Ke > >_______________________________________________ >Xen-devel mailing list >Xen-devel@lists.xensource.com >http://lists.xensource.com/xen-devel > >