On 11/21/23 03:01, Namhyung Kim wrote: > On Mon, Nov 13, 2023 at 3:26 AM James Clark <james.clark@xxxxxxx> wrote: >> Add documentation for the new Perf event open parameters and >> the threshold_max capability file. >> >> Signed-off-by: James Clark <james.clark@xxxxxxx> >> --- >> Documentation/arch/arm64/perf.rst | 56 +++++++++++++++++++++++++++++++ >> 1 file changed, 56 insertions(+) >> >> diff --git a/Documentation/arch/arm64/perf.rst b/Documentation/arch/arm64/perf.rst >> index 1f87b57c2332..36b8111a710d 100644 >> --- a/Documentation/arch/arm64/perf.rst >> +++ b/Documentation/arch/arm64/perf.rst >> @@ -164,3 +164,59 @@ and should be used to mask the upper bits as needed. >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/arm64/tests/user-events.c >> .. _tools/lib/perf/tests/test-evsel.c: >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/perf/tests/test-evsel.c >> + >> +Event Counting Threshold >> +========================================== >> + >> +Overview >> +-------- >> + >> +FEAT_PMUv3_TH (Armv8.8) permits a PMU counter to increment only on >> +events whose count meets a specified threshold condition. For example if >> +threshold_compare is set to 2 ('Greater than or equal'), and the >> +threshold is set to 2, then the PMU counter will now only increment by >> +when an event would have previously incremented the PMU counter by 2 or >> +more on a single processor cycle. >> + >> +To increment by 1 after passing the threshold condition instead of the >> +number of events on that cycle, add the 'threshold_count' option to the >> +commandline. >> + >> +How-to >> +------ >> + >> +The threshold, threshold_compare and threshold_count values can be >> +provided per event: >> + >> +.. code-block:: sh >> + >> + perf stat -e stall_slot/threshold=2,threshold_compare=2/ \ >> + -e dtlb_walk/threshold=10,threshold_compare=3,threshold_count/ > Can you please explain this a bit more? > > I guess the first event counts stall_slot PMU if the event if it's > greater than or equal to 2. And as threshold_count is not set, > it'd count the stall_slot as is. E.g. it counts 3 when it sees 3. Hence without 'threshold_count' being set, the other two config requests will not have an effect, is that correct ? > > OTOH, dtlb_walk will count 1 if it sees an event less than 10. > Is my understanding correct? 'Equals' and 'Greater-than-or-equal' makes sense and are intuitive. Just wondering what will happen for 'Not-equal' and 'Less-than' - when would the counter count in such cases ? 0: Not-equal 1: Equals 2: Greater-than-or-equal 3: Less-than
