Re: [RFC PATCH 03/10] perf workqueue: add threadpool start and stop functions

[Namhyung Kim <namhyung@kernel.org>]

On Tue, Jul 13, 2021 at 5:11 AM Riccardo Mancini <rickyman7@gmail.com> wrote:
>
> This patch adds the start and stop functions, alongside the thread
> function.
> Each thread will run until a stop signal is received.
> Furthermore, start and stop are added to the test.
>
> Thread management is based on the prototype from Alexey:
> https://lore.kernel.org/lkml/cover.1625227739.git.alexey.v.bayduraev@linux.intel.com/
>
> Suggested-by: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
> Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
> ---
>  tools/perf/tests/workqueue.c           |  13 ++
>  tools/perf/util/workqueue/threadpool.c | 238 +++++++++++++++++++++++++
>  tools/perf/util/workqueue/threadpool.h |   5 +
>  3 files changed, 256 insertions(+)
>
> diff --git a/tools/perf/tests/workqueue.c b/tools/perf/tests/workqueue.c
> index 1bd4d78c13eb3b14..be377e9897bab4e9 100644
> --- a/tools/perf/tests/workqueue.c
> +++ b/tools/perf/tests/workqueue.c
> @@ -10,16 +10,29 @@ struct threadpool_test_args_t {
>
>  static int __threadpool__prepare(struct threadpool_struct **pool, int pool_size)
>  {
> +       int ret;
> +
>         *pool = create_threadpool(pool_size);
>         TEST_ASSERT_VAL("threadpool creation failure", *pool != NULL);
>         TEST_ASSERT_VAL("threadpool size is wrong",
>                         threadpool_size(*pool) == pool_size);
>
> +       ret = start_threadpool(*pool);
> +       TEST_ASSERT_VAL("threadpool start failure", ret == 0);
> +       TEST_ASSERT_VAL("threadpool is not ready", threadpool_is_ready(*pool));
> +
>         return 0;
>  }
>
>  static int __threadpool__teardown(struct threadpool_struct *pool)
>  {
> +       int ret;
> +
> +       ret = stop_threadpool(pool);
> +       TEST_ASSERT_VAL("threadpool start failure", ret == 0);

s/start/stop/

> +       TEST_ASSERT_VAL("stopped threadpool is ready",
> +                       !threadpool_is_ready(pool));
> +
>         destroy_threadpool(pool);
>
>         return 0;
> diff --git a/tools/perf/util/workqueue/threadpool.c b/tools/perf/util/workqueue/threadpool.c
> index 70c67569f956a3e2..f4635ff782b9388e 100644
> --- a/tools/perf/util/workqueue/threadpool.c
> +++ b/tools/perf/util/workqueue/threadpool.c
[SNIP]
> +/**
> + * wait_thread - receive ack from thread
> + *
> + * NB: call only from main thread!
> + */
> +static int wait_thread(struct thread_struct *thread)
> +{
> +       int res;
> +       enum thread_msg msg = THREAD_MSG__UNDEFINED;
> +
> +       res = read(thread->pipes.from[0], &msg, sizeof(msg));
> +       if (res < 0) {

Maybe it needs to handle -EINTR.


> +               pr_err("threadpool: failed to recv msg from tid=%d: %s\n",
> +                      thread->tid, strerror(errno));
> +               return -1;
> +       }
> +       if (msg != THREAD_MSG__ACK) {
> +               pr_err("threadpool: received unexpected msg from tid=%d: %s\n",
> +                      thread->tid, thread_msg_tags[msg]);
> +               return -1;
> +       }
> +
> +       pr_debug2("threadpool: received ack from tid=%d\n", thread->tid);
> +
> +       return 0;
> +}
> +
> +/**
> + * terminate_thread - send stop signal to thread and wait for ack
> + *
> + * NB: call only from main thread!
> + */
> +static int terminate_thread(struct thread_struct *thread)
> +{
> +       int res;
> +       enum thread_msg msg = THREAD_MSG__STOP;
> +
> +       res = write(thread->pipes.to[1], &msg, sizeof(msg));
> +       if (res < 0) {
> +               pr_err("threadpool: error sending stop msg to tid=%d: %s\n",
> +                       thread->tid, strerror(errno));
> +               return res;
> +       }
> +
> +       res = wait_thread(thread);
> +
> +       return res;
> +}
> +
> +/**
> + * threadpool_thread - function running on thread
> + *
> + * This function waits for a signal from main thread to start executing
> + * a task.
> + * On completion, it will go back to sleep, waiting for another signal.
> + * Signals are delivered through pipes.
> + */
> +static void *threadpool_thread(void *args)
> +{
> +       struct thread_struct *thread = (struct thread_struct *) args;
> +       enum thread_msg msg;
> +       int err;
> +
> +       thread->tid = gettid();
> +
> +       pr_debug2("threadpool[%d]: started\n", thread->tid);
> +
> +       for (;;) {
> +               msg = THREAD_MSG__ACK;
> +               err = write(thread->pipes.from[1], &msg, sizeof(msg));
> +               if (err == -1) {
> +                       pr_err("threadpool[%d]: failed to send ack: %s\n",
> +                               thread->tid, strerror(errno));
> +                       break;
> +               }
> +
> +               msg = THREAD_MSG__UNDEFINED;
> +               err = read(thread->pipes.to[0], &msg, sizeof(msg));
> +               if (err < 0) {
> +                       pr_err("threadpool[%d]: error receiving msg: %s\n",
> +                               thread->tid, strerror(errno));
> +                       break;
> +               }
> +
> +               if (msg != THREAD_MSG__WAKE && msg != THREAD_MSG__STOP) {
> +                       pr_err("threadpool[%d]: received unexpected msg: %s\n",
> +                               thread->tid, thread_msg_tags[msg]);
> +                       break;
> +               }
> +
> +               if (msg == THREAD_MSG__STOP)
> +                       break;
> +       }
> +
> +       pr_debug2("threadpool[%d]: exit\n", thread->tid);
> +
> +       msg = THREAD_MSG__ACK;
> +       err = write(thread->pipes.from[1], &msg, sizeof(msg));
> +       if (err == -1) {
> +               pr_err("threadpool[%d]: failed to send ack: %s\n",
> +                       thread->tid, strerror(errno));
> +               return NULL;
> +       }
> +
> +       return NULL;
> +}
> +
>  /**
>   * create_threadpool - create a fixed threadpool with @n_threads threads
>   */
> @@ -173,3 +306,108 @@ int threadpool_size(struct threadpool_struct *pool)
>  {
>         return pool->nr_threads;
>  }
> +
> +/**
> + * __start_threadpool - start all threads in the pool.
> + *
> + * This function does not change @pool->status.
> + */
> +static int __start_threadpool(struct threadpool_struct *pool)
> +{
> +       int t, tt, ret = 0, nr_threads = pool->nr_threads;
> +       sigset_t full, mask;
> +       pthread_t handle;
> +       pthread_attr_t attrs;
> +
> +       sigfillset(&full);
> +       if (sigprocmask(SIG_SETMASK, &full, &mask)) {
> +               pr_err("Failed to block signals on threads start: %s\n",
> +                       strerror(errno));
> +               return -1;
> +       }
> +
> +       pthread_attr_init(&attrs);
> +       pthread_attr_setdetachstate(&attrs, PTHREAD_CREATE_DETACHED);
> +
> +       for (t = 0; t < nr_threads; t++) {
> +               struct thread_struct *thread = &pool->threads[t];
> +
> +               if (pthread_create(&handle, &attrs, threadpool_thread, thread)) {
> +                       for (tt = 1; tt < t; tt++)
> +                               terminate_thread(thread);
> +                       pr_err("Failed to start threads: %s\n", strerror(errno));
> +                       ret = -1;
> +                       goto out_free_attr;
> +               }
> +
> +               if (wait_thread(thread)) {
> +                       for (tt = 1; tt <= t; tt++)
> +                               terminate_thread(thread);
> +                       ret = -1;
> +                       goto out_free_attr;
> +               }
> +       }

Isn't it better doing this way?

for (t = 0; t < nr_threads; t++) {
    pthread_create(t)
}

for (t = 0; t < nr_threads; t++) {
    wait_thread(t)
}

Thanks,
Namhyung


> +
> +out_free_attr:
> +       pthread_attr_destroy(&attrs);
> +
> +       if (sigprocmask(SIG_SETMASK, &mask, NULL)) {
> +               pr_err("Failed to unblock signals on threads start: %s\n",
> +                       strerror(errno));
> +               ret = -1;
> +       }
> +
> +       return ret;
> +}
> +