Mateusz Guzik <mjguzik@gmail.com> says: The clone side contends against exit side in a way which avoidably exacerbates the problem by the latter waiting on locks held by the former while holding the tasklist_lock. Whacking this for both add_device_randomness and pids allocation gives me a 15% speed up for thread creation/destruction in a 24-core vm. The random patch is worth about 4%. The new bottleneck is pidmap_lock itself, with the biggest problem being the allocation itself taking the lock *twice*. Bench (plop into will-it-scale): $ cat tests/threadspawn1.c char *testcase_description = "Thread creation and teardown"; static void *worker(void *arg) { return (NULL); } void testcase(unsigned long long *iterations, unsigned long nr) { pthread_t thread; int error; while (1) { error = pthread_create(&thread, NULL, worker, NULL); assert(error == 0); error = pthread_join(thread, NULL); assert(error == 0); (*iterations)++; } } * patches from https://lore.kernel.org/r/20250206164415.450051-1-mjguzik@gmail.com: pid: drop irq disablement around pidmap_lock pid: perform free_pid() calls outside of tasklist_lock pid: sprinkle tasklist_lock asserts exit: hoist get_pid() in release_task() outside of tasklist_lock exit: perform add_device_randomness() without tasklist_lock Link: https://lore.kernel.org/r/20250206164415.450051-1-mjguzik@gmail.com Signed-off-by: Christian Brauner <brauner@kernel.org>