From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754146AbcIBOPr (ORCPT ); Fri, 2 Sep 2016 10:15:47 -0400 Received: from smtprelay0147.hostedemail.com ([216.40.44.147]:38305 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751752AbcIBOPq (ORCPT ); Fri, 2 Sep 2016 10:15:46 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1539:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2691:2693:3138:3139:3140:3141:3142:3352:3622:3865:3867:3871:3874:4250:5007:6119:6120:6261:7514:7875:7901:10004:10400:10848:10967:11232:11658:11914:12740:13069:13311:13357:13439:14181:14659:14721:21067:21080:30054:30070:30090:30091,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:2,LUA_SUMMARY:none X-HE-Tag: shame30_6c216c721141c X-Filterd-Recvd-Size: 1763 Date: Fri, 2 Sep 2016 10:15:41 -0400 From: Steven Rostedt To: Stefan Hajnoczi Cc: Luiz Capitulino , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com, mhiramat@kernel.org, mtosatti@redhat.com Subject: Re: [PATCH 4/4] kvm: x86: export TSC offset to user-space Message-ID: <20160902101541.2b670b09@gandalf.local.home> In-Reply-To: <20160902134301.GC21771@stefanha-x1.localdomain> References: <1472663145-1835-1-git-send-email-lcapitulino@redhat.com> <1472663145-1835-5-git-send-email-lcapitulino@redhat.com> <20160902134301.GC21771@stefanha-x1.localdomain> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2 Sep 2016 09:43:01 -0400 Stefan Hajnoczi wrote: > Can TSC offset changes occur at runtime? > > One example is vcpu hotplug where the tracing tool would need to fetch > the new vcpu's TSC offset after tracing has already started. > > Another example is if QEMU or the guest change the TSC offset while > running. If the tracing tool doesn't notice this then trace events will have > incorrect timestamps. I believe there are tracepoints for these events. They would obviously need to be enabled for the tracer to catch them. I would also recommend that they go into their own instance to make sure other events do not overwrite them. -- Steve