linux-kernel - Re: [PATCH v2] perf test workload: Add thread count argument to thloop

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Message-ID: <aQEpdjP5OwU73q64@x1>
Date: Tue, 28 Oct 2025 17:37:10 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf test workload: Add thread count argument to
 thloop

On Tue, Oct 28, 2025 at 12:55:56PM -0700, Ian Rogers wrote:
> On Tue, Oct 28, 2025 at 12:13 PM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > On Tue, Oct 28, 2025 at 08:38:20AM -0700, Ian Rogers wrote:
> > > Allow the number of threads for the thloop workload to be increased
> > > beyond the normal 2. Add error checking to the parsed time and thread
> > > count values.
> > >
> > > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > > ---
> > > v2: Perform the pthread_join unconditionally and ensure started
> > >     threads terminate.
> > > ---
> > >  tools/perf/tests/workloads/thloop.c | 45 ++++++++++++++++++++++++-----
> > >  1 file changed, 38 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/tools/perf/tests/workloads/thloop.c b/tools/perf/tests/workloads/thloop.c
> > > index 457b29f91c3e..bd8168f883fb 100644
> > > --- a/tools/perf/tests/workloads/thloop.c
> > > +++ b/tools/perf/tests/workloads/thloop.c
> > > @@ -31,21 +31,52 @@ static void *thfunc(void *arg)
> > >
> > >  static int thloop(int argc, const char **argv)
> > >  {
> > > -     int sec = 1;
> > > -     pthread_t th;
> > > +     int nt = 2, sec = 1, err = 1;
> > > +     pthread_t *thread_list = NULL;
> > >
> > >       if (argc > 0)
> > >               sec = atoi(argv[0]);
> > >
> > > +     if (sec <= 0) {
> > > +             fprintf(stderr, "Error: seconds (%d) must be >= 1\n", sec);
> > > +             return 1;
> > > +     }
> > > +
> > > +     if (argc > 1)
> > > +             nt = atoi(argv[1]);
> > > +
> > > +     if (nt <= 0) {
> > > +             fprintf(stderr, "Error: thread count (%d) must be >= 1\n", nt);
> > > +             return 1;
> > > +     }
> > > +
> > >       signal(SIGINT, sighandler);
> > >       signal(SIGALRM, sighandler);
> > > -     alarm(sec);
> > >
> > > -     pthread_create(&th, NULL, thfunc, test_loop);
> > > -     test_loop();
> > > -     pthread_join(th, NULL);
> > > +     thread_list = calloc(nt, sizeof(pthread_t));
> > > +     if (thread_list == NULL) {
> > > +             fprintf(stderr, "Error: malloc failed for %d threads\n", nt);
> > > +             goto out;
> > > +     }
> > > +     for (int i = 1; i < nt; i++) {
> >
> > Why do you start at 1? What goes in thread[0]? calloc() leaves it at
> > NULL, then if you have two threads you'll allocate thread[1], i gets
> > incremented, 2 < 2 fails, you get just one thread created, when two were
> > asked?
> >
> > Oh, I see, you use the main thread to run, that test_loop() just before
> > the err = 0, its just that you allocate thread[0] for nothing, that
> > confused me.
> 
> Agreed. It was so I could avoid doing "nt-1" as I mentioned before.
> Fwiw, pthread_self will sometimes return 0 for the main thread and so
> it isn't entirely inconsistent to do things this way. Not that the
> main thread should try to do a pthread_join with itself.

:-)

Its just a test,

Acked-by: Arnaldo Carvalho de Melo <acme@...hat.com>
 
> Thanks,
> Ian
> 
> > - Arnaldo
> >
> > > +             int ret = pthread_create(&thread_list[i], NULL, thfunc, test_loop);
> > >
> > > -     return 0;
> > > +             if (ret) {
> > > +                     fprintf(stderr, "Error: failed to create thread %d\n", i);
> > > +                     done = 1; // Ensure started threads terminate.
> > > +                     goto out;
> > > +             }
> > > +     }
> > > +     alarm(sec);
> > > +     test_loop();
> > > +     err = 0;
> > > +out:
> > > +     for (int i = 1; i < nt; i++) {
> > > +             if (thread_list && thread_list[i])
> > > +                     pthread_join(thread_list[i], /*retval=*/NULL);
> > > +     }
> > > +     free(thread_list);
> > > +     return err;
> > >  }
> > >
> > >  DEFINE_WORKLOAD(thloop);
> > > --
> > > 2.51.1.851.g4ebd6896fd-goog