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Reshmi_Mitra

Beginner

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06-13-2010
02:32 PM

38 Views

Difference between events & samples

I tried looking for any difference between events and samples but could not find a definitive answer.

Secondly, is there any why to find out number of times any (stall causing) event has occurred? For example, I am measuring RESOURCE_STALLS.ANY. I know how many cycles have been spent in various events. But, I would like to know how many times the samples were taken.

Thanks in advance,

Reshmi

7 Replies

Reshmi_Mitra

Beginner

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06-13-2010
03:38 PM

38 Views

Hi,

Another way of asking the same question above.

I ran VTUNE for finding out RESOURCE_STALLS.ANY for my FFT code. Here is the results I got:

Samples: 9.071E+5

Events: 9.071E+10

%age: 87.87%

Does this mean that every time there is some kind of RESOURCE_STALLS activity, there is a latency of 1E+05 cycles? This seems like an unrealistic figure.

I am trying to find an average number of stall cycles every time there is a stall in the pipeline.

regards,

Reshmi

TimP

Black Belt

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06-13-2010
05:02 PM

38 Views

Presumably, this means you had set the sample after value to 1e5.

Reshmi_Mitra

Beginner

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06-14-2010
06:58 AM

38 Views

But, can you please tell me how this will help me calculate:

1- number of cycles spent on RESOURCE_STALLS

2- how many times RESOURCE_STALLS actually occurs?

Thanks,

Reshmi

Thomas_W_Intel

Employee

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06-14-2010
02:16 PM

38 Views

Why you are seeing resource stalls and howmuchthis impactsyour application depends on a lotof factors. You might want touseUOPS_EXECUTED.CORE_STALL_CYCLES to measure thenumber of cycles where no op is executed. This can serve as a starting point to estimate how often the out-of-order engine is actually stalled.The Performance Analysis Guide for Intel Core i7 Processor and Intel Xeon 5500 processors can give you further guidance on how to analyze the application.

Reshmi_Mitra

Beginner

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06-16-2010
04:23 PM

38 Views

Thanks for your reply. And you have confirmed that my approach about the cycle count is correct.

I am not trying to tune the application. I am creating an analytical model which takes inputs from Vtune data. I need to find probability values based on the data provided.So, I need to find average stalls of multiple events.. or how many times the samples are taken.

Somehow, I am still not able to get how many times a particular stall event e.g. resources or branches or others are occurring. Any thoughts on that will be greatly appreciated.

Thomas_W_Intel

Employee

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06-18-2010
02:16 AM

38 Views

Reshmi_Mitra

Beginner

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06-18-2010
05:48 AM

38 Views

Thanks. I will go over the paper.

For more complete information about compiler optimizations, see our Optimization Notice.