On 23/11/2023 15:45, James Clark wrote: > > > On 23/11/2023 05:50, Anshuman Khandual wrote: >> >> >> 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 ? > > Yeah I can mention this. It's implied because 0 is the default value of > config fields, and 0 is a valid value for compare and count field, so > threshold=0 has to be the way to disable it. But I can mention it > explicitly. > To avoid any confusion, I thought you meant threshold here instead of threshold_count. But I replied in more detail about the same issue on patch 2.
