Messages in this thread | | | Subject | Re: Problem running perf using Intel-PT with snapshots | From | Nadav Amit <> | Date | Thu, 18 May 2023 10:56:02 -0700 |
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> On May 18, 2023, at 12:52 AM, Adrian Hunter <adrian.hunter@intel.com> wrote: > > On 18/05/23 07:26, Nadav Amit wrote: >> Hello perf masters, >> >> I am running perf with Intel PT with snapshot mode and the result makes no >> sense. I tried to figure it out myself but failed. >> >> Excluding the first data file, the rest seem messed up in various ways. The >> only thing that repeatedly shows are calls to __fentry__+0x0. I would note >> that ftrace is not enabled, and I turned off mitigations as I thought it >> might somehow be related, but it did not help. >> >> Here is an example for execution and output. In between I ran >> `kill -SIGUSR2 [perf-pid]`. To dump some traces. >> >> Any ideas what it might be? >> >> Thanks, >> Nadav >> >> -- >> >> $ perf record -e intel_pt/noretcomp=1/k --kcore --timestamp -a --snapshot=e262144 --switch-output -m,64 > > --switch-output does not work well with Intel PT. Intel PT needs all of the sideband event information from all files, so decoding errors result from splitting files. > > If you need separate files, consider stopping and restarting 'perf record' instead. If you do that, you may want to look at options like -B and -N and --no-bpf-event which can affect how long it takes to stop perf record. > > If you don't need separate files, you can use --time to look at time ranges within the resulting perf.data file.
Thank you Adrian. It was driving me crazy and I was sure I am somehow not accounting for some ftrace/rethunk or some other binary rewriting event.
These ideas for workarounds should suffice.
Thanks again, Nadav
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