Hi Marcelo,
Can you please write a succint but complete description of the method so it can be verified?Sure. - Prerequisite 1. the host TSC is synchronized and stable. 2. kvm_write_tsc_offset events include previous and next TSC offset values. 3. Every event's trace_clock is TSC. - Assumption for the sake of ease 1. One VCPU 2. The guest executes no write_tsc or write_tsc only once. - Configuration 1. On the host, kvm_exit/entry events are recorded in the buffer A and kvm_write_tsc_offset events are recorded in the buffer B. 2. Boot a guest - Sort method 1. Confirm which the kvm_write_tsc_offset events are recorded except for boot. Note that a vcpu thread writes TSC offset when boot as an initial operation. 1-1. If not recorded, it means that the guest did not execute write_tsc. So, we convert the guest TSC to the host TSC using TSC offset of boot. => END 1-2. If recorded, it means that the guest executed write_tsc. So, we use new kvm_write_tsc_offset event information. 2. We convert the host TSC(Th) of the kvm_write_tsc_offset event to the guest TSC(Tg) using previous_tsc_offset value: Tg = Th + previous_tsc_offset 3. To search the point where the guest executed write_tsc, we find "n" which satisfies the condition Tn < Tg < Tn+1 or Tn+1 < Tn < Tg from older events of the guest. The former condition means trace data of the guest were recorded monotonically. On the other hand, the latter condition means trace data of the guest moved backward. 4. We convert the guest TSC of trace data to the host TSC using previous_tsc_offset value before "n" and using next_tsc_offset value after "n+1". => END - Note We assumed one vcpu and no write_tsc or write_tsc only once for the sake of ease. For other conditions, we will use similar method. Thanks,There is no certainty. Consider the following information available guest trace host trace 100: guest_tsc_write (tsc_offset=-100 => guest_tsc = 0) 104: guest_tsc_write (tsc_offset=-104 => guest_tsc = 0) 108: guest_tsc_write (tsc_offset=-108 => guest_tsc = 0) 1: eventA 2: eventB 3: eventC 1: eventD 2: eventE 3: eventF How can you tell which tsc_offset to use for eventD ? It could be either -104 or -108. The notion of "next_tsc_offset" is subject to such issue. I suppose its fine to restrict the interface as follows: the tool will accept one trace of events with monotonic timestamps and the user is responsible for correlating that to a host trace.
OK, I'll add the restriction, which trace data must have monotonic timestamps to use this feature. I think guests seldom will execute write_tsc, so in many cases, timestamps will be monotonically recorded in trace data.
That is, you can't feed distinct instances of guest kernel trace.
I'm not clear for "distinct instances". Is this about SMP or multiple guests? Would you explain about this? Thanks, -- Yoshihiro YUNOMAE Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: yoshihiro.yunomae.ez@xxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
