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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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@google.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.

- 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