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From: "Guy Harris" <guy@xxxxxxxxxxxx>
Sent: Friday, January 15, 2010 3:20 PM
To: "Community support list for Wireshark" <wireshark-users@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-users] Timestamp Skew
On Jan 15, 2010, at 3:04 PM, Gianluca Varenni wrote:
It's not documented, and depends on the version of Windows, the service
pack, and the HAL type... Most of the times it's a non-compensated RDTSC,
however.
If it's just RDTSC, wouldn't it have the same problems on "SpeedStep
machines" as raw RDTSC? The description in the mail was
The documentation for KeQueryPerformanceCounter doesn't say anything about
that. So it's entirely possible that they do something under the hood to
prevent this issue.
Have a nice day
GV
Possible values are
a.. 0 (default) -> Timestamps generated through
KeQueryPerformanceCounter, less reliable on SMP/HyperThreading machines,
precision = some microseconds
b.. 2 -> Timestamps generated through KeQuerySystemTime, more reliable
on SMP/HyperThreading machines, precision = scheduling quantum (10/15 ms)
c.. 3 -> Timestamps generated through the i386 instruction RDTSC, less
reliable on SMP/HyperThreading/SpeedStep machines, precision = some
microseconds
Also, should it say "machines where the clock rate is variable" or
something such as that? I don't know whether Intel still calls it
"SpeedStep", and AMD have their own names for it.
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