Hi Cody, On Wed, Feb 05, 2025 at 02:56:03PM -0500, Cody Tapscott wrote: > Re-sending due to bad e-mail client settings that introduced artificial > line wraps. > > My apologies for the confusion. Thanks! No problem. > > Signed-off-by: Cody Tapscott <cody@xxxxxxxxxxx> > > -- > > The man page recommends re-scaling event counts as (value * time_enabled > / time_running), but does not mention that some time-filters (esp. > exclude_kernel and exclude_user) do not affect the reported time_enabled or > time_running, causing a very noisy estimate of the true event count. > > This limitation is easy to encounter when profiling events that are dominated > by kernel (>= 50%) vs. user time and which are relatively short compared to > the PMU muxing frequency (<~10x the period). In those cases, it is common to > see (time_running / time_enabled) report, e.g., ~50% active time when perhaps > almost none of the user time was actually spent with the counter running. > --- > man/man2/perf_event_open.2 | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/man/man2/perf_event_open.2 b/man/man2/perf_event_open.2 > index bcc6a39cb..bc22a3b12 100644 > --- a/man/man2/perf_event_open.2 > +++ b/man/man2/perf_event_open.2 > @@ -1063,9 +1063,22 @@ .SS Arguments > .TP > .I exclude_user > If this bit is set, the count excludes events that happen in user space. > +.IP > +Note this does not affect the I'd remove 'note', which is usually superfluous. Just start with 'This does not affect ...". > +.I time_running > +or > +.I time_enabled > +fields, so enabling this may impact the reliability of the estimated total counts in the presence of multiplexing. Sorry for not mentioning this. We also have 80-col right margin. So, you'll need to break this line, but at a phrase boundary. I'd break between 'of' and 'the', I think. I'd also break after the comma. fields, so enabling this may impact the reliability of the estimated total counts in the presence of multiplexing. > .TP > .I exclude_kernel > If this bit is set, the count excludes events that happen in kernel space. > +.IP > +Note this does not affect the Same about 'note'. > +.I time_running > +or > +.I time_enabled > +fields, > +so enabling this may impact the reliability of the estimated total counts in the presence of multiplexing. > .TP > .I exclude_hv > If this bit is set, the count excludes events that happen in the > @@ -1677,6 +1690,16 @@ .SS Reading results > and > .I time running > values can be used to scale an estimated value for the count. > +.IP > +Note that for most events these values are not affected by Same about 'note that'. Have a lovely day! Alex > +.IR exclude_hv , > +.IR exclude_idle , > +.IR exclude_user , > +or > +.I exclude_kernel > +and, > +if these are enabled, > +the scaled estimate may be significantly less reliable in the presence of multiplexing. > .TP > .I value > An unsigned 64-bit value containing the counter result. > -- > 2.34.1 > > -- <https://www.alejandro-colomar.es/>
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