Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751852Ab3FGFWb (ORCPT ); Fri, 7 Jun 2013 01:22:31 -0400 Received: from mail9.hitachi.co.jp ([133.145.228.44]:48842 "EHLO mail9.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751056Ab3FGFW3 (ORCPT ); Fri, 7 Jun 2013 01:22:29 -0400 X-AuditID: 85900ec0-d60ccb900000151e-64-51b16e12d1d1 Message-ID: <51B16E0E.5020208@hitachi.com> Date: Fri, 07 Jun 2013 14:22:22 +0900 From: Yoshihiro YUNOMAE User-Agent: Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120604 Thunderbird/13.0 MIME-Version: 1.0 To: Gleb Natapov , Marcelo Tosatti Cc: 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: [PATCH V2 1/1] kvm/vmx: Add a tracepoint write_tsc_offset References: <20130604083616.22713.24922.stgit@yunodevel> <20130604083619.22713.25360.stgit@yunodevel> <20130606002322.GA24351@amt.cnet> <20130606113305.GB4725@redhat.com> In-Reply-To: <20130606113305.GB4725@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4820 Lines: 120 (2013/06/06 20:33), Gleb Natapov wrote: > On Wed, Jun 05, 2013 at 09:23:22PM -0300, Marcelo Tosatti wrote: >> On Tue, Jun 04, 2013 at 05:36:19PM +0900, Yoshihiro YUNOMAE wrote: >>> Add a tracepoint write_tsc_offset for tracing TSC offset change. >>> We want to merge ftrace's trace data of guest OSs and the host OS using >>> TSC for timestamp in chronological order. We need "TSC offset" values for >>> each guest when merge those because the TSC value on a guest is always the >>> host TSC plus guest's TSC offset. If we get the TSC offset values, we can >>> calculate the host TSC value for each guest events from the TSC offset and >>> the event TSC value. The host TSC values of the guest events are used when we >>> want to merge trace data of guests and the host in chronological order. >>> (Note: the trace_clock of both the host and the guest must be set x86-tsc in >>> this case) >>> >>> TSC offset is stored in the VMCS by vmx_write_tsc_offset() or >>> vmx_adjust_tsc_offset(). KVM executes the former function when a guest boots. >>> The latter function is executed when kvm clock is updated. Only host can read >>> TSC offset value from VMCS, so a host needs to output TSC offset value >>> when TSC offset is changed. >>> >>> Since the TSC offset is not often changed, it could be overwritten by other >>> frequent events while tracing. To avoid that, I recommend to use a special >>> instance for getting this event: >>> >>> 1. set a instance before booting a guest >>> # cd /sys/kernel/debug/tracing/instances >>> # mkdir tsc_offset >>> # cd tsc_offset >>> # echo x86-tsc > trace_clock >>> # echo 1 > events/kvm/kvm_write_tsc_offset/enable >>> >>> 2. boot a guest >>> >>> Signed-off-by: Yoshihiro YUNOMAE >>> Cc: Marcelo Tosatti >>> Cc: Gleb Natapov >>> Cc: Thomas Gleixner >>> Cc: Ingo Molnar >>> Cc: "H. Peter Anvin" >>> --- >>> arch/x86/kvm/trace.h | 18 ++++++++++++++++++ >>> arch/x86/kvm/vmx.c | 3 +++ >>> arch/x86/kvm/x86.c | 1 + >>> 3 files changed, 22 insertions(+) >>> >>> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h >>> index fe5e00e..9c22e39 100644 >>> --- a/arch/x86/kvm/trace.h >>> +++ b/arch/x86/kvm/trace.h >>> @@ -815,6 +815,24 @@ TRACE_EVENT(kvm_track_tsc, >>> __print_symbolic(__entry->host_clock, host_clocks)) >>> ); >>> >>> +TRACE_EVENT(kvm_write_tsc_offset, >>> + TP_PROTO(__u64 previous_tsc_offset, __u64 next_tsc_offset), >>> + TP_ARGS(previous_tsc_offset, next_tsc_offset), >>> + >>> + TP_STRUCT__entry( >>> + __field( __u64, previous_tsc_offset ) >>> + __field( __u64, next_tsc_offset ) >>> + ), >>> + >>> + TP_fast_assign( >>> + __entry->previous_tsc_offset = previous_tsc_offset; >>> + __entry->next_tsc_offset = next_tsc_offset; >>> + ), >>> + >>> + TP_printk("previous=%llu next=%llu", >>> + __entry->previous_tsc_offset, __entry->next_tsc_offset) >>> +); >>> + >> >> Yoshihiro YUNOMAE, >> >> 1) Why is previous_tsc_offset necessary? I was considering the situations where we did not enable kvm_write_tsc_offset event before booting a guest or where we did not use multiple buffers. Here, we will need another new I/F to get current TSC offset of a given VCPU. For example, if kvm_write_tsc_offset is not included in the host's trace data, we get the current TSC offset from the new I/F and apply it to all guest events. On the other hand, if kvm_write_tsc_offset event appears more than once, we apply the previous offset to guest events before the first TSC offset change. Since we support only for using multiple buffers now, we don't need to record previous TSC offset at this time. But I'm conscious that we have to change the format of kvm_write_tsc_offset event when we support those situations. >> 2) The TSC offset traces should include vcpu number, so that its >> possible to correlate traces of SMP guests (the tool should use >> the individual vcpu tsc offsets when converting guests trace). >> > Why PID is not enough? No other trace, except kvm_entry, outputs vcpu id. As Gleb mentioned, a tool can understand TSC offset for each vcpu from PID and vcpu number of kvm_entry. IMO, that is indirect way, so I would be better off including vcpu number. >> 3) Please add traces for svm.c. Sure, I'll add the tracepoint for SVM. Thanks, Yoshihiro YUNOMAE -- Yoshihiro YUNOMAE Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: yoshihiro.yunomae.ez@hitachi.com -- 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/