Messages in this thread | | | Subject | Re: [PATCH 1/1] perf/x86: Fix time_shift in perf_event_mmap_page | From | Adrian Hunter <> | Date | Mon, 19 Oct 2015 11:46:48 +0300 |
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On 19/10/15 11:08, Ingo Molnar wrote: > > * Adrian Hunter <adrian.hunter@intel.com> wrote: > >> Commit b20112edeadf ("perf/x86: Improve accuracy of perf/sched clock") >> allowed the time_shift value in perf_event_mmap_page to be as much >> as 32. Unfortunately the documented algorithms for using time_shift >> have it shifting an integer, whereas to work correctly with the value >> 32, the type must be u64. >> >> Fix by limiting the shift to 31 and adjusting the multiplier accordingly. >> >> Also update the documentation of perf_event_mmap_page so that new code >> based on it will be more future-proof. >> >> Fixes: b20112edeadf ("perf/x86: Improve accuracy of perf/sched clock") >> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> > > Would be nice to point out via what symptoms the code misbehaves and how users > notice.
In the case of perf tools, Intel PT decodes correctly but the timestamps that are output (for example by perf script) have lost 32-bits of granularity so they look like they are not changing at all.
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