How to improve sampling frequency

[Jasonmessage]

Hi joemario，

Now，i‘m using the perf c2c tool, but i find that sample size is small，following is the setting parameter.

perf_event_max_sample_rate ： 100000
perf_cpu_time_max_percent ：25
command line ：perf c2c record -F 60000 -a --all-user sleep 5
the output sample size : 5321
the hardware : X86 40 cores
test case : false_sharing_example.c

I don't know why the output sample size is so small , so need your help!
Looking forward to your reply soon when you are convenient!

[joemario]

Hi Jason:
Try this:
gcc -g false_sharing_example.c -pthread -lnuma -o false_sharing.exe
perf c2c record -F ./false_sharing.exe 40
Then hit ctrlC after 2-3 seconds.

Joe

[Jasonmessage]

Thank joemario for your reply! but we test the program by your advice！ The result is still not good and the output sample size : 14K (time : ctrlC after 8 seconds , perf_event_max_sample_rate ： 100000)

[joemario]

Hi Jason:
Can you attach your c2c report output file?
Joe

[joemario]

Hi Jason:
A few more thoughts to consider.
14K samples for just that program or for just user space (--all-user) is nothing to worry about. That is sufficient. Remember, C2C only samples load and store instructions. And by default, it will ignore all loads with a load latency of less than 30 machine cycles. You can adjust that 30 to whatever you want, but less than 30 is not interesting.
Joe