[EXT] Re: [PATCH v6 1/4] lib: add generic support for reading PMU events

[Morten Brørup]

> From: Tomasz Duszynski [mailto:tduszynski at marvell.com]
> Sent: Thursday, 26 January 2023 16.28
> 
> >From: Bruce Richardson <bruce.richardson at intel.com>
> >Sent: Thursday, January 26, 2023 1:59 PM
> >
> >Other possible complication is - how does this work with threads that
> are not pinned to a
> >particular physical core? Do things work as expected in that case?
> >
> 
> It's assumed that once set of counters is enabled on particular l-core
> then this thread shouldn't be migrating
> back and for the obvious reasons.
> 
> But, once scheduled elsewhere all should still work as expected.

Just to elaborate what Tomasz stated here...

The patch contains this line (code comments are mine):

return syscall(SYS_perf_event_open, &attr, /*pid*/ 0, /*cpu*/ -1, group_fd, 0);

And man 2 perf_event_open [1] says:

pid == 0 and cpu == -1:
	This measures the calling process/thread on any CPU.

So it should work just fine, even when a thread is not pinned to a particular physical core.

[1]: https://man7.org/linux/man-pages/man2/perf_event_open.2.html