VirtualBox 4.2.4 on FreeBSD 9.1-PRERELEASE problem: VMs behave very different when pinned to different cores

[Andriy Gapon]

on 25/11/2012 19:57 Andriy Gapon said the following:
> on 24/11/2012 00:17 Alex Chistyakov said the following:
>> I collected two samples and put them here: http://1888.spb.ru/samples.zip
>> sched-cpu0.ktr is for a VM running on CPU #0 and sched-cpu1.ktr is for
>> a VM running on CPU #1
>> They seem to be very different.
> 
> It looks like you didn't stop ktr tracing before running ktrdump or something
> like that.  schedgraph can not grok the files because it believes that the
> timestamps are incorrect.
> 
> # - While the workload is continuing (i.e. before it finishes), disable
> #   KTR tracing by setting 'sysctl debug.ktr.mask=0'.  This is necessary
> #   to avoid a race condition while running ktrdump, i.e. the KTR ring buffer
> #   will cycle a bit while ktrdump runs, and this confuses schedgraph because
> #   the timestamps appear to go backwards at some point.

Hmm, looks like this assessment is not correct.
I now think that the root cause of schedgraph issue might be a too wild
difference in what TSC counters produce on different (logical/physical) CPUs.

E.g.:
131059   1   33232414877586 ...
131058   1   33232414876546 ...
131057   3   33232416064514 ...
131056   3   33232416064198 ...

Or even:
131038   0   33232862369416 ...
131037   3   33232409671570 ...
131036   0   33232862367256 ...
131035   3   33232409670982 ...

That's 455111586 ticks!

> Could you please also provide the CPU identification block from dmesg?

This is even more interesting now.

-- 
-- 
Andriy Gapon