[Xen-devel] Problem correlating TSC read from domU with Xentrace's TSC

[Thawan Kooburat <kthawan@xxxxxxxxx>]

Hi,

I am trying to correlating performance issue in guest VM with the
scheduling trace from Xentrace. User-mode application in guest VM
periodically dump APIC ID and RDTSC into trace. I also start Xentrace
in Dom0 during the same period.

However, I notice that range of TSC values report both trace is
completely disjointed. TSC values from Xentrace is always greater than
what  guest VM see, even if I start capturing Xen's trace 30s before
capturing trace in guest VM.

I understand that Xen don't emulate rdtsc() for PV guest and Xentrace
also read rdtsc() during __insert_record(). However, I don't
understand what cause my issue.  Any suggestion?   I am using Xen
4.1.1 on Fedora 15


-- 
Thawan Kooburat

Graduate Student
Department of Computer Science
UW-Madison

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