Messages in this thread | | | Date | Thu, 6 Jun 2013 14:33:06 +0300 | From | Gleb Natapov <> | Subject | Re: [PATCH V2 1/1] kvm/vmx: Add a tracepoint write_tsc_offset |
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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 <yoshihiro.yunomae.ez@hitachi.com> > > Cc: Marcelo Tosatti <mtosatti@redhat.com> > > Cc: Gleb Natapov <gleb@redhat.com> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: "H. Peter Anvin" <hpa@zytor.com> > > --- > > 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? > > 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.
> 3) Please add traces for svm.c.
-- Gleb.
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