Re: [PATCH 4/4] perf python: Add counting.py as example for counting perf events

[Gautam Menghani]

On Thu, May 01, 2025 at 09:04:43AM -0700, Ian Rogers wrote:
> On Thu, May 1, 2025 at 2:37 AM Gautam Menghani <gautam@xxxxxxxxxxxxx> wrote:
> >
> > Add counting.py - a python version of counting.c to demonstrate
> > measuring and reading of counts for given perf events.
> >
> > Signed-off-by: Gautam Menghani <gautam@xxxxxxxxxxxxx>
> > ---
> >  tools/perf/python/counting.py | 41 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> >  create mode 100755 tools/perf/python/counting.py
> >
> > diff --git a/tools/perf/python/counting.py b/tools/perf/python/counting.py
> > new file mode 100755
> > index 000000000000..0c58907bd8bf
> > --- /dev/null
> > +++ b/tools/perf/python/counting.py
> > @@ -0,0 +1,41 @@
> > +#!/usr/bin/env python3
> > +# SPDX-License-Identifier: GPL-2.0
> > +# -*- python -*-
> > +# -*- coding: utf-8 -*-
> > +
> > +import perf
> > +
> > +def main():
> > +        cpus = perf.cpu_map()
> > +        thread_map = perf.thread_map(-1)
> > +        evlist = perf.evlist(cpus, thread_map)
> > +
> > +        evsel1 = perf.evsel(type = perf.TYPE_SOFTWARE,
> > +                 config = perf.COUNT_SW_CPU_CLOCK,
> > +                 read_format = perf.FORMAT_TOTAL_TIME_ENABLED | perf.FORMAT_TOTAL_TIME_RUNNING,
> > +                 disabled=1)
> > +        evlist.add(evsel1)
> > +
> > +        evsel2 = perf.evsel(type = perf.TYPE_SOFTWARE,
> > +                 config = perf.COUNT_SW_TASK_CLOCK,
> > +                 read_format = perf.FORMAT_TOTAL_TIME_ENABLED | perf.FORMAT_TOTAL_TIME_RUNNING,
> > +                 disabled=1)
> > +        evlist.add(evsel2)
> 
> Nice example! Would this be better as:
> ```
>     cpus    = perf.cpu_map()
>     threads = perf.thread_map(-1)
>     evlist = perf.parse_events("cpu-clock,task-clock", cpus, threads)
> ```
> If you run `perf stat -vv -e 'cpu-clock,task-clock' .. ` you can
> double check the perf event attribute bits. For example in
> tracepoint.py we remove the SAMPLE_IP:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/python/tracepoint.py?h=perf-tools-next#n27

Yes this is cleaner, will fix in v2.

> 
> > +
> > +        evlist.open()
> > +        evlist.enable()
> > +
> > +        count = 100000
> > +        while count > 0:
> > +            count -= 1
> > +
> > +        evlist.disable()
> > +        evsel = evlist.next(None)
> > +        while evsel != None:
> > +            counts = evsel.read(0, 0)
> 
> Rather than just reading on the first CPU and thread, perhaps change
> to iterate over the cpus and threads? Something like:
> ```
>     for evsel in evlist:
>         for cpu in cpus:
>             for thread in threads:
>                 counts = evsel.read(cpu, thread)
>                 print(f"For {evsel} read val={counts.val}
> enable={counts.ena} run ={counts.run}")
> ```

Ack, will do

Thanks,
Gautam