Re: [PATCH v2] perf bench: Use condition variables in numa.

[Jiri Olsa]

On Mon, Oct 12, 2020 at 09:16:11AM -0700, Ian Rogers wrote:

SNIP

> @@ -483,6 +484,18 @@ static void init_global_mutex(pthread_mutex_t *mutex)
>  	pthread_mutex_init(mutex, &attr);
>  }
>  
> +/*
> + * Return a process-shared (global) condition variable:
> + */
> +static void init_global_cond(pthread_cond_t *cond)
> +{
> +	pthread_condattr_t attr;
> +
> +	pthread_condattr_init(&attr);
> +	pthread_condattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
> +	pthread_cond_init(cond, &attr);
> +}
> +
>  static int parse_cpu_list(const char *arg)
>  {
>  	p0.cpu_list_str = strdup(arg);
> @@ -1136,15 +1149,18 @@ static void *worker_thread(void *__tdata)
>  	if (g->p.serialize_startup) {
>  		pthread_mutex_lock(&g->startup_mutex);
>  		g->nr_tasks_started++;
> +		/* The last thread wakes the main process. */
> +		if (g->nr_tasks_started == g->p.nr_tasks)
> +			pthread_cond_signal(&g->startup_cond);

should you remove the condition? it's not necessary
and making this racy, no?

just single pthread_cond_signal should be enough,
because the wait code is checking the number of tasks

jirka