Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753250Ab3FJU27 (ORCPT ); Mon, 10 Jun 2013 16:28:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37752 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753078Ab3FJU25 (ORCPT ); Mon, 10 Jun 2013 16:28:57 -0400 Date: Mon, 10 Jun 2013 17:28:23 -0300 From: Marcelo Tosatti To: Gleb Natapov Cc: Yoshihiro YUNOMAE , linux-kernel@vger.kernel.org, "H. Peter Anvin" , David Sharp , Steven Rostedt , Hidehiro Kawai , Ingo Molnar , yrl.pp-manager.tt@hitachi.com, Masami Hiramatsu , Thomas Gleixner Subject: Re: Re: Re: [PATCH V2 1/1] kvm/vmx: Add a tracepoint write_tsc_offset Message-ID: <20130610202823.GC31409@amt.cnet> References: <20130604083616.22713.24922.stgit@yunodevel> <20130604083619.22713.25360.stgit@yunodevel> <20130606002322.GA24351@amt.cnet> <20130606113305.GB4725@redhat.com> <51B16E0E.5020208@hitachi.com> <20130609111442.GP4725@redhat.com> <51B59CC2.3060707@hitachi.com> <20130610100505.GB4725@redhat.com> <20130610140424.GA25632@amt.cnet> <20130610163834.GG29022@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130610163834.GG29022@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2684 Lines: 62 On Mon, Jun 10, 2013 at 07:38:34PM +0300, Gleb Natapov wrote: > > Guest traces contain vcpu number and not pid (because guest is unaware > > of host PID). > > > No, guest trace is just a regular ftrace done inside a guest. It contains > guest's PIDs which is useless for host. # tracer: nop # # entries-in-buffer/entries-written: 5333/5333 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | Traces contain CPU ID. > I do not know how exactly guest traces are transfered to a host, if > each vcpu buffer is transfered separately host can figure out what > trace entry belong to which vcpu based on what buffer the trace is in. > But the information about what buffer belongs to which vcpu id should > be transfered to a host somehow too. > > > > > However, when we > > > > focus on output data of the write_tsc_offset event, it is difficult to > > > > directly understand contents of the data if vcpu number information is > > > > not included. So, including the information is useful, I think. > > > > > > > How your tool does it now? > > > > It merges guest trace with host trace (by converting the TSC timestamp > > in the guest trace to host TSC using tsc_offset information). > > > I mean how it does it now without vcpu id. The answer is that it works > for only one vcpu now. Yes. > > By not recording vcpu ID in the tsc_offset trace, it is necessary to > > supply the tool with PID<->VCPU_id tuples for translation (so its an > > additional step required, and it makes trace merge impossible > > if the information is not available). > The tool needs PID<->VCPU_id tuples to do the merging of any trace > entry. Without that it does not know how to interpret entry timestamps > (which offset to use). Apparently it will get this information from > vmentry trace point. What is so special about tsc_offset tracing that > it needs to contain vcpuid by itself. If the tsc_offset tracepoint contains vcpu ID, its possible to lookup guest trace entry (which contains CPU ID), and match on that. Without that, PID<->VCPU_id tuples are necessary. Yes? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/