From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [RFC] Physical hot-add cpus and TSC Date: Thu, 27 May 2010 09:44:04 +0100 Message-ID: References: <789F9655DD1B8F43B48D77C5D30659731E78D370@shsmsx501.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <789F9655DD1B8F43B48D77C5D30659731E78D370@shsmsx501.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: "Jiang, Yunhong" , Dan Magenheimer , "Xen-Devel (xen-devel@lists.xensource.com)" , Ian Pratt List-Id: xen-devel@lists.xenproject.org On 27/05/2010 07:15, "Jiang, Yunhong" wrote: >>>> get synced up before host software gets a look in. I don't think we can >>>> comment on whether or not there is an issue here without more >>>> information. > > Yes, this is a issue. The TSC will not be synched by firmware when hot-added, > at least I didn't find any spec on this, and my experiment shows the TSC value > is very small when new CPU is brought up. We need sync it in Xen side, > > Is it possible to sync the new-added CPU with the BSP when the CPU is added > (changed from non-present to present), as Keir suggested in previous mail? I > will have a look on the related code. I implemented this as xen-unstable:21468. This represents a strict improvement on what was in xen-unstable before that (no tsc sync at all, ever, because I deleted it about a week ago). Open to further improvements, if we can get consensus. -- Keir