topic Weird BTS Performance in Intel® ISA Extensions

Weird BTS Performance

cwillems — Fri, 10 Jun 2011 14:25:53 GMT

Hi,

I am playing around with the BTS feature and observe a very huge performance penalty. It is said in several places that this is normal. On the other hand I see academic publications that use this feature which report only a very small overhead.

Therefore, I have performed several experiments on different CPUs with different DebugCtl settings and different kind of memory caching types.

What me confuses the most is the fact that experiments with only the TR-flag enabled are *much* slower than those with TR-flag *and* BTS-flag enabled. From my understanding enabling TR+BTS does "more" than only TR, in fact writing the BTM not only to the system bus but also to the DebugStore.

Am I wrong? What is the reason for this "strange" observation?

Thanks a lot for your help,
Carsten

Weird BTS Performance

SHIH_K_Intel — Fri, 10 Jun 2011 23:04:56 GMT

Branch Trace isdesigned to help tools to profile/diagnose. It can capture a lot of information, and the associated costs (delays) goes with the amount/freqency your tool ask the HW to capture. In-frequent sampling would incur smaller overhead. Doing it frequently would be like attaching a exhaust emission analyzer to the car's tail pipe, it won't be able to drive normally or normal gas mileage.

Weird BTS Performance

cwillems — Tue, 14 Jun 2011 10:23:43 GMT

Thank you for your answer.
Unfortunately, I cannot see how it is related to my particular question.

Cheers
Carsten

Weird BTS Performance

TimP — Tue, 14 Jun 2011 19:14:04 GMT

Perhaps you didn't tell us how your question relates to this forum.

Weird BTS Performance

cwillems — Wed, 15 Jun 2011 12:56:37 GMT

Hi Tim,

I am sorry if I have used the wrong one. I just have searched for similar requests and found some in this forum. Is their a better suited for BTM/PerformanceMonitoring-related questions?

Cheers & Thanks
Carsten

Weird BTS Performance

Hussam_Mousa__Intel_ — Fri, 30 Sep 2011 22:23:02 GMT

Can you please post your question to this forum:

http://software.intel.com/en-us/forums/platform-monitoring/