Monitoring different processes using PAPI_overflow

[Mariana Barros]

Hello,

I am trying to monitor different processes running in the machine using PAPI_overflow. In order to do that, I list all the PIDs from the processes currently running, and, for each one, I create and add events to an eventset, set an overflow, and try to attach this eventset to the PID. However, even though the code compiles and runs without raising any errors, the overflows are only triggered for the monitoring process, and not for any other one. 

Does anyone know if it is possible to use PAPI_overflow to monitor different external processes? And if so, how should I proceed?

Thank you in advance.

[Anthony Danalis]

Hello,

Unfortunately, "PAPI can not be attached to thread or cpu if overflowing" (per papi.c:2900). Do you need to use overflow for your monitoring? Could you not sample the counters in a loop?

Thanks,

Anthony

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[Phil Mucci]

Hi all,

I may have written that line of code long ago - a time when we were maintaining our own kernel patch for the PMU available on the Pentium Pro - Linux was only 5 years old - and we did overflow / multiplexing in user space 😳

Today’s reality is that the Linux kernel perf subsystem supports third party overflow / profiling semantics. The latter is actually what you are after - you don’t want to be delivering a signal to a second process on every overflow - you want to read a buffer of addresses where overflow occurred (aka the perf sample buffer).

I’m going to wager there’s not a huge implementation lift should someone want to follow the code path through. 

If you want to just profile a code using PAPI, rather than writing your own infra, hpctoolkit could do what you are after.

Hope this helps,

On May 19, 2025, at 18:21, Anthony Danalis <adan...@icl.utk.edu> wrote:



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