Commit f892f9f9 authored by David Carlier's avatar David Carlier Committed by Tejun Heo
Browse files

tools/sched_ext: scx_userland: fix data races on shared counters 



The stats thread reads nr_vruntime_enqueues, nr_vruntime_dispatches,
nr_vruntime_failed, and nr_curr_enqueued concurrently with the main
thread writing them, with no synchronization.

Use __atomic builtins with relaxed ordering for all accesses to these
counters to eliminate the data races.

Only display accuracy is affected, not scheduling correctness.

Signed-off-by: default avatarDavid Carlier <devnexen@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 625be345

tools/sched_ext/scx_userland.c

+13 −13
Original line number Diff line number Diff line
@@ -157,9 +157,9 @@ static int dispatch_task(__s32 pid) 


	err = bpf_map_update_elem(dispatched_fd, NULL, &pid, 0);

	if (err) {

		nr_vruntime_failed++;

		__atomic_add_fetch(&nr_vruntime_failed, 1, __ATOMIC_RELAXED);

	} else {

		nr_vruntime_dispatches++;

		__atomic_add_fetch(&nr_vruntime_dispatches, 1, __ATOMIC_RELAXED);

	}



	return err;
@@ -202,8 +202,8 @@ static int vruntime_enqueue(const struct scx_userland_enqueued_task *bpf_task) 
		return ENOENT;



	update_enqueued(curr, bpf_task);

	nr_vruntime_enqueues++;

	nr_curr_enqueued++;

	__atomic_add_fetch(&nr_vruntime_enqueues, 1, __ATOMIC_RELAXED);

	__atomic_add_fetch(&nr_curr_enqueued, 1, __ATOMIC_RELAXED);



	/*

	 * Enqueue the task in a vruntime-sorted list. A more optimal data
@@ -279,9 +279,9 @@ static void dispatch_batch(void) 
			LIST_INSERT_HEAD(&vruntime_head, task, entries);

			break;

		}

		nr_curr_enqueued--;

		__atomic_sub_fetch(&nr_curr_enqueued, 1, __ATOMIC_RELAXED);

	}

	skel->bss->nr_scheduled = nr_curr_enqueued;

	skel->bss->nr_scheduled = __atomic_load_n(&nr_curr_enqueued, __ATOMIC_RELAXED);

}



static void *run_stats_printer(void *arg)
@@ -306,9 +306,9 @@ static void *run_stats_printer(void *arg) 
		printf("|-----------------------|\n");

		printf("| VRUNTIME / USER       |\n");

		printf("|-----------------------|\n");

		printf("|  enq:      %10llu |\n", nr_vruntime_enqueues);

		printf("|  disp:     %10llu |\n", nr_vruntime_dispatches);

		printf("|  failed:   %10llu |\n", nr_vruntime_failed);

		printf("|  enq:      %10llu |\n", __atomic_load_n(&nr_vruntime_enqueues, __ATOMIC_RELAXED));

		printf("|  disp:     %10llu |\n", __atomic_load_n(&nr_vruntime_dispatches, __ATOMIC_RELAXED));

		printf("|  failed:   %10llu |\n", __atomic_load_n(&nr_vruntime_failed, __ATOMIC_RELAXED));

		printf("o-----------------------o\n");

		printf("\n\n");

		fflush(stdout);
@@ -376,10 +376,10 @@ static void bootstrap(char *comm) 
{

	exit_req = 0;

	min_vruntime = 0.0;

	nr_vruntime_enqueues = 0;

	nr_vruntime_dispatches = 0;

	nr_vruntime_failed = 0;

	nr_curr_enqueued = 0;

	__atomic_store_n(&nr_vruntime_enqueues, 0, __ATOMIC_RELAXED);

	__atomic_store_n(&nr_vruntime_dispatches, 0, __ATOMIC_RELAXED);

	__atomic_store_n(&nr_vruntime_failed, 0, __ATOMIC_RELAXED);

	__atomic_store_n(&nr_curr_enqueued, 0, __ATOMIC_RELAXED);

	memset(tasks, 0, pid_max * sizeof(*tasks));

	LIST_INIT(&vruntime_head);