perf_event_open cpu should be -1 for valid PID #1464
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mmat11
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May 11, 2024
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I'm missing context, sorry. What is currently broken? Can you extend the commit message to include the explanation? And is it possible to add a test? |
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Theoretically, if you specify a PID then the arguments given mean it is applying only to CPU 0. In practice, it may not be affecting anything because the perf <-> tracepoint/kprobe linkage has some gaps. |
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Hmm, could this be the cause of #406 ? |
I believe not, in that test |
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So this is a fix for a theoretical issue? Happy to carry the patch without tests as long as the commit message gets a bit of detail why we're doing this. |
From perf_event_open manpage attributes documentation:
pid > 0 and cpu == -1
This measures the specified process/thread on any CPU.
Fixes it so it measures all CPUs when a PID is specified.
Signed-off-by: Bryce Kahle <bryce.kahle@datadoghq.com>
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Updated commit message |
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This will match libbpf behavior. Relevant snippet from
perf_event_openmanpage