From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Magenheimer Subject: RE: Problem correlating TSC read from domU with Xentrace's TSC Date: Wed, 16 Nov 2011 15:51:14 -0800 (PST) Message-ID: <2650416a-630f-45b7-956e-f45a81e81f0f@default> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable 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: Thawan Kooburat , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org > I am trying to correlating performance issue in guest VM with the > scheduling trace from Xentrace. User-mode application in guest VM > periodically dump APIC ID and RDTSC into trace. I also start Xentrace > in Dom0 during the same period. >=20 > However, I notice that range of TSC values report both trace is > completely disjointed. TSC values from Xentrace is always greater than > what guest VM see, even if I start capturing Xen's trace 30s before > capturing trace in guest VM. >=20 > I understand that Xen don't emulate rdtsc() for PV guest and Xentrace > also read rdtsc() during __insert_record(). However, I don't > understand what cause my issue. Any suggestion? I am using Xen > 4.1.1 on Fedora 15 Hi Thawan -- Depending on the underlying hardware, Xen may emulate rdtsc for PV guests. To force this off, set tsc_mode=3D2 in your guest vm.cfg file (and reboot). For more info on tsc_mode see tscmode.txt in the Xen source tree (or google for it). Dan