[Bug translator/13820] New: timer.profile(NNN) variant using perf probes

[Bug translator/13820] New: timer.profile(NNN) variant using perf probes

[fche at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=13820

             Bug #: 13820
           Summary: timer.profile(NNN) variant using perf probes
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
        AssignedTo: systemtap@sourceware.org
        ReportedBy: fche@redhat.com
    Classification: Unclassified


It would be nice to have some syntactic sugar implemented in the
translator to present a profiling/backtrace-capable probe point
at arbitrary frequencies, and implement them in terms of 
perf.hw.cpu_cycles (unscaled variant if possible), related to
the cpu core speed and the script-requested Hz rate.

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[Bug translator/13820] timer.profile(NNN) variant using perf probes

[fche at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=13820

--- Comment #1 from Frank Ch. Eigler <fche at redhat dot com> 2012-03-08 01:48:28 UTC ---
e.g.

  probe timer.profile.hz(997) { }

could map on a 2000 MHz core to perf.hw.cpu_clock

  probe perf.type(0).config(0).sample(2006018) { }

(where 2006018 would be 2,000,000,000 / 997).
This would have to be calculated at module startup time.
And it may be that we'd actually need a more complicated
function, or even some sort of baby PLL, to approximate
the desired frequency.

It would probably be unwise to map timer.{hz,ms,etc.}(NNN)
to this because this uses up scarce resources, so can't be
unprivileged-safe.

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[Bug translator/13820] timer.profile(NNN) variant using perf probes

[flu at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=13820

Felix Lu <flu at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |flu at redhat dot com
         Resolution|---                         |FIXED

--- Comment #2 from Felix Lu <flu at redhat dot com> ---
Added a probe point timer.profile.freq.hz(N).

This is only accurate up to 100 hz.

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