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No support for fractional sampling intervals?

scorp007
Beginner
176 Views
It seems like neither VTune nor VTune Amp Xe support sampling intervals of less than 1 ms.

What if I'd like to sample my application twice every millisecond? I.e. Sample every 0.5 ms.

No go, it seems.

This looks like a major oversight, as every other decent profiler (including free CodeAnalyst) supports this simple requirement.

What is the rationale behind this?
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2 Replies
Vladimir_T_Intel
Moderator
176 Views

Suppose you have a machine with 2GHz CPU. By setting the SAV=2000000 for CPU clockticks event in the EBS analysis of VTune or Lightweight Hotspot analysis of VTune Amplifier XE, you get 1 sample per ms. This is statistically reasonable sampling rate for most cases. Playing with the SAV towards decrease allows to increase the sampling frequency. But be careful setting too low SAV - the system may hang in oft-recurring hardware interruption handling.

Mark_D_Intel
Employee
176 Views
Note that there are two different types of sampling technology used in VTune Amplifier XE
1. User mode sampling - each sample collects the call stack for each thread - this has a minimum sampling interval of 1ms due to overhead concerns.
2. Hardware-event sampling - Vladimir addressed how to lower the sampling interval in his reply
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