Greetings!!!!

 

I have a query on Oprofile sampling rate for the event “CPU_CLK” on a powerpc core running at 1GHz core clock. Please help me here.

 

We did following Oprofile experiment by varying Oprofile test run duration and varying CPU_CLK sampling rate:

 

a)      Oprofile test run duration for:

ü  10 secs and

ü  100secs.

b)      CPU_CLK sampling rate variation and tried following sampling rates:

·         1000us (default)

·         1100us

·         500us

·         250us

·         50us

  

But there are some observations where we want your help:

 

All the data referred below is generated for a IP traffic of around 90MBPS for an Evolved Packet System scenario:

 

·         Reference Data with default sampling rate (1000us) and default oprofile test run duration (i.e. ~10sec).

Ø  With Oprofile Sampling Rate = 1000us (default) and oprofile test duration of ~10secs:

o   The total samples collected by Oprofile sampler = 10686.

 

·         Experiment Data with varying sampling rate and oprofile test run duration increased (i.e. ~100sec).

Ø  With Oprofile Sampling Rate = 1000us (default) and oprofile test duration of ~100secs:

o   The total samples collected by oprofile sampler = 28121.

Ø  With Oprofile Sampling Rate = 1100us and oprofile test duration of ~100secs:

o   The total samples collected by oprofile sampler = 26313.

Ø  With Oprofile Sampling Rate = 500us and oprofile test duration of ~100secs:

o   The total samples collected by oprofile sampler = 25463.

Ø  With Oprofile Sampling Rate = 250us and oprofile test duration of ~100secs:

o   The total samples collected by oprofile sampler = 26858.

Ø  With Oprofile Sampling Rate = 50us and oprofile test duration of ~100secs:

o   The total samples collected by oprofile sampler = 22759.

 

The doubt where we need your help is following:

 

·         How do we relate “total samples collected” and “sampling rate” with the “oprofile test run duration”?

o   I am giving below some data based on the oprofile results:

1.       The total samples collected by oprofiler sampler with 1000us (default) sampling rate (running for ~10sec) = 10686.

·         10686 * 1000us = 10686000us = 10.686 secs. (This calculation approx matches with the oprofile test run duration i.e. 10sec)

2.       The total samples collected by oprofiler sampler with 50us sampling rate (running for ~100sec) = 22759.

·         22759 * 50us = 1137950us = 1.13795 secs. (This doesn’t match (with the same calculation done in step#1) with oprofile test run duration i.e. 100sec).

 

Thanks & Regards,

Amit.