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Groups > linux.kernel > #1250461
| From | Adrian Hunter <adrian.hunter@intel.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 1/1] perf/x86: Fix time_shift in perf_event_mmap_page |
| Date | 2015-10-19 10:50 +0200 |
| Message-ID | <qleiK-7D6-13@gated-at.bofh.it> (permalink) |
| References | <qkdf5-7zE-31@gated-at.bofh.it> <qkdf5-7zE-45@gated-at.bofh.it> <qldG1-6ST-21@gated-at.bofh.it> |
| Organization | Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki |
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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[PATCH 0/1] perf/x86: Fix time_shift in perf_event_mmap_page Adrian Hunter <adrian.hunter@intel.com> - 2015-10-16 15:30 +0200
[PATCH 1/1] perf/x86: Fix time_shift in perf_event_mmap_page Adrian Hunter <adrian.hunter@intel.com> - 2015-10-16 15:30 +0200
Re: [PATCH 1/1] perf/x86: Fix time_shift in perf_event_mmap_page Ingo Molnar <mingo@kernel.org> - 2015-10-19 10:10 +0200
Re: [PATCH 1/1] perf/x86: Fix time_shift in perf_event_mmap_page Adrian Hunter <adrian.hunter@intel.com> - 2015-10-19 10:50 +0200
Re: [PATCH 1/1] perf/x86: Fix time_shift in perf_event_mmap_page Ingo Molnar <mingo@kernel.org> - 2015-10-19 13:30 +0200
[PATCH V2 1/1] perf/x86: Fix time_shift in perf_event_mmap_page Adrian Hunter <adrian.hunter@intel.com> - 2015-10-19 14:10 +0200
[tip:perf/core] perf/x86: Fix time_shift in perf_event_mmap_page tip-bot for Adrian Hunter <tipbot@zytor.com> - 2015-10-20 11:40 +0200
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