* Adrian Hunter <[email protected]> wrote:
> On 19/10/15 11:08, Ingo Molnar wrote:
> >
> > * Adrian Hunter <[email protected]> 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 <[email protected]>
> >
> > 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.
Sounds like a nice and very informative paragraph to add to the changelog! :-)
Thanks,
Ingo
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