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// SPDX-License-Identifier: GPL-2.0
/*
* Verify that ops.dequeue() is called for tasks leaving BPF custody through
* an SCX-internal cross-CPU migration (move_remote_task_to_local_dsq()).
*
* Copyright (c) 2026 Google LLC.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <time.h>
#include <sched.h>
#include <bpf/bpf.h>
#include <scx/common.h>
#include <sys/wait.h>
#include "scx_test.h"
#include "dequeue_remote.bpf.skel.h"
#define MAX_WORKERS 64
#define RUN_MS 2000
static int nr_cpus;
static long long now_ms(void)
{
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
return ts.tv_sec * 1000LL + ts.tv_nsec / 1000000;
}
/* mix of short bursts and sleeps to generate lots of enqueues and wakeups */
static void worker_fn(int id)
{
long long end = now_ms() + RUN_MS;
volatile unsigned long sum = 0;
while (now_ms() < end) {
unsigned long j;
for (j = 0; j < 20000 + id * 1000; j++)
sum += j;
if (id & 1)
usleep(100);
else
sched_yield();
}
exit(0);
}
static enum scx_test_status run_scenario(struct dequeue_remote *skel,
bool use_move_to_local,
const char *name)
{
enum scx_test_status ret = SCX_TEST_PASS;
struct bpf_link *link;
pid_t pids[MAX_WORKERS];
int nr_workers, nr_forked, i;
nr_workers = 2 * nr_cpus;
if (nr_workers < 4)
nr_workers = 4;
if (nr_workers > MAX_WORKERS)
nr_workers = MAX_WORKERS;
skel->bss->test_use_move_to_local = use_move_to_local;
skel->bss->enqueue_cnt = 0;
skel->bss->dequeue_cnt = 0;
skel->bss->dispatch_dequeue_cnt = 0;
skel->bss->change_dequeue_cnt = 0;
skel->bss->remote_dispatch_cnt = 0;
skel->bss->remote_running_cnt = 0;
skel->bss->missed_dequeue_cnt = 0;
skel->bss->core_sched_exec_dequeue_cnt = 0;
memset(&skel->data->uei, 0, sizeof(skel->data->uei));
link = bpf_map__attach_struct_ops(skel->maps.dequeue_remote_ops);
SCX_FAIL_IF(!link, "Failed to attach struct_ops for %s", name);
fflush(stdout);
fflush(stderr);
for (nr_forked = 0; nr_forked < nr_workers; nr_forked++) {
pid_t pid = fork();
if (pid < 0) {
SCX_ERR("Failed to fork worker %d", nr_forked);
ret = SCX_TEST_FAIL;
break;
}
if (pid == 0)
worker_fn(nr_forked);
pids[nr_forked] = pid;
}
/* on failure, kill the remaining workers but still reap them */
for (i = 0; i < nr_forked; i++) {
int status;
if (ret != SCX_TEST_PASS)
kill(pids[i], SIGKILL);
if (waitpid(pids[i], &status, 0) != pids[i]) {
SCX_ERR("Failed to wait for worker %d", i);
ret = SCX_TEST_FAIL;
} else if (ret == SCX_TEST_PASS && status != 0) {
SCX_ERR("Worker %d exited with status %d", i, status);
ret = SCX_TEST_FAIL;
}
}
bpf_link__destroy(link);
if (ret != SCX_TEST_PASS)
return ret;
printf("%s:\n", name);
printf(" workers: %d\n", nr_workers);
printf(" enqueues: %lu\n", (unsigned long)skel->bss->enqueue_cnt);
printf(" dequeues: %lu (dispatch: %lu, property_change: %lu)\n",
(unsigned long)skel->bss->dequeue_cnt,
(unsigned long)skel->bss->dispatch_dequeue_cnt,
(unsigned long)skel->bss->change_dequeue_cnt);
if (!use_move_to_local)
printf(" remote SCX_DSQ_LOCAL_ON dispatches: %lu\n",
(unsigned long)skel->bss->remote_dispatch_cnt);
printf(" ran on a CPU other than the enqueue CPU: %lu\n",
(unsigned long)skel->bss->remote_running_cnt);
printf(" ran without ops.dequeue(): %lu\n",
(unsigned long)skel->bss->missed_dequeue_cnt);
printf(" late SCX_DEQ_CORE_SCHED_EXEC dequeues: %lu\n",
(unsigned long)skel->bss->core_sched_exec_dequeue_cnt);
if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_UNREG))
SCX_ERR("Scheduler exited with kind=%lld: %s",
(long long)skel->data->uei.kind, skel->data->uei.msg);
SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_UNREG));
/* the test is meaningless if no task was moved across CPUs */
SCX_GT(skel->bss->remote_running_cnt, 0);
SCX_EQ(skel->bss->enqueue_cnt, skel->bss->dequeue_cnt);
return SCX_TEST_PASS;
}
static enum scx_test_status setup(void **ctx)
{
struct dequeue_remote *skel;
cpu_set_t cpus;
SCX_FAIL_IF(sched_getaffinity(0, sizeof(cpus), &cpus),
"Failed to get CPU affinity");
nr_cpus = CPU_COUNT(&cpus);
if (nr_cpus < 2) {
fprintf(stderr, "Skipping: requires at least 2 usable CPUs\n");
return SCX_TEST_SKIP;
}
skel = SCX_OPS_OPEN(dequeue_remote_ops, dequeue_remote);
SCX_OPS_LOAD(skel, dequeue_remote_ops, dequeue_remote, uei);
*ctx = skel;
return SCX_TEST_PASS;
}
static enum scx_test_status run(void *ctx)
{
struct dequeue_remote *skel = ctx;
enum scx_test_status status;
status = run_scenario(skel, false,
"BPF queue -> SCX_DSQ_LOCAL_ON | cpu");
if (status != SCX_TEST_PASS)
return status;
status = run_scenario(skel, true,
"user DSQ -> scx_bpf_dsq_move_to_local()");
if (status != SCX_TEST_PASS)
return status;
return SCX_TEST_PASS;
}
static void cleanup(void *ctx)
{
struct dequeue_remote *skel = ctx;
dequeue_remote__destroy(skel);
}
struct scx_test dequeue_remote_test = {
.name = "dequeue_remote",
.description = "Verify ops.dequeue() on SCX-internal cross-CPU migrations",
.setup = setup,
.run = run,
.cleanup = cleanup,
};
REGISTER_SCX_TEST(&dequeue_remote_test)
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