linux/tools/testing/selftests/bpf/test_kmods/bpf_test_rqspinlock.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/prandom.h>
#include <linux/ktime.h>
#include <asm/rqspinlock.h>
#include <linux/perf_event.h>
#include <linux/kthread.h>
#include <linux/atomic.h>
#include <linux/slab.h>

static struct perf_event_attr hw_attr = {
	.type		= PERF_TYPE_HARDWARE,
	.config		= PERF_COUNT_HW_CPU_CYCLES,
	.size		= sizeof(struct perf_event_attr),
	.pinned		= 1,
	.disabled	= 1,
	.sample_period	= 100000,
};

static rqspinlock_t lock_a;
static rqspinlock_t lock_b;
static rqspinlock_t lock_c;

#define RQSL_SLOW_THRESHOLD_MS 10
static const unsigned int rqsl_hist_ms[] = {
	1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
	12, 14, 16, 18, 20, 25, 30, 40, 50, 75,
	100, 150, 200, 250, 1000,
};
#define RQSL_NR_HIST_BUCKETS ARRAY_SIZE(rqsl_hist_ms)

enum rqsl_context {
	RQSL_CTX_NORMAL = 0,
	RQSL_CTX_NMI,
	RQSL_CTX_MAX,
};

struct rqsl_cpu_hist {
	atomic64_t hist[RQSL_CTX_MAX][RQSL_NR_HIST_BUCKETS];
	atomic64_t success[RQSL_CTX_MAX];
	atomic64_t failure[RQSL_CTX_MAX];
};

static DEFINE_PER_CPU(struct rqsl_cpu_hist, rqsl_cpu_hists);

enum rqsl_mode {
	RQSL_MODE_AA = 0,
	RQSL_MODE_ABBA,
	RQSL_MODE_ABBCCA,
};

static int test_mode = RQSL_MODE_AA;
module_param(test_mode, int, 0644);
MODULE_PARM_DESC(test_mode,
		 "rqspinlock test mode: 0 = AA, 1 = ABBA, 2 = ABBCCA");

static int normal_delay = 20;
module_param(normal_delay, int, 0644);
MODULE_PARM_DESC(normal_delay,
		 "rqspinlock critical section length for normal context (20ms default)");

static int nmi_delay = 10;
module_param(nmi_delay, int, 0644);
MODULE_PARM_DESC(nmi_delay,
		 "rqspinlock critical section length for NMI context (10ms default)");

static struct perf_event **rqsl_evts;
static int rqsl_nevts;

static struct task_struct **rqsl_threads;
static int rqsl_nthreads;
static atomic_t rqsl_ready_cpus = ATOMIC_INIT(0);

static int pause = 0;

static const char *rqsl_mode_names[] = {
	[RQSL_MODE_AA] = "AA",
	[RQSL_MODE_ABBA] = "ABBA",
	[RQSL_MODE_ABBCCA] = "ABBCCA",
};

struct rqsl_lock_pair {
	rqspinlock_t *worker_lock;
	rqspinlock_t *nmi_lock;
};

static struct rqsl_lock_pair rqsl_get_lock_pair(int cpu)
{
	int mode = READ_ONCE(test_mode);

	switch (mode) {
	default:
	case RQSL_MODE_AA:
		return (struct rqsl_lock_pair){ &lock_a, &lock_a };
	case RQSL_MODE_ABBA:
		if (cpu & 1)
			return (struct rqsl_lock_pair){ &lock_b, &lock_a };
		return (struct rqsl_lock_pair){ &lock_a, &lock_b };
	case RQSL_MODE_ABBCCA:
		switch (cpu % 3) {
		case 0:
			return (struct rqsl_lock_pair){ &lock_a, &lock_b };
		case 1:
			return (struct rqsl_lock_pair){ &lock_b, &lock_c };
		default:
			return (struct rqsl_lock_pair){ &lock_c, &lock_a };
		}
	}
}

static u32 rqsl_hist_bucket_idx(u32 delta_ms)
{
	int i;

	for (i = 0; i < RQSL_NR_HIST_BUCKETS; i++) {
		if (delta_ms <= rqsl_hist_ms[i])
			return i;
	}

	return RQSL_NR_HIST_BUCKETS - 1;
}

static void rqsl_record_lock_result(u64 delta_ns, enum rqsl_context ctx, int ret)
{
	struct rqsl_cpu_hist *hist = this_cpu_ptr(&rqsl_cpu_hists);
	u32 delta_ms = DIV_ROUND_UP_ULL(delta_ns, NSEC_PER_MSEC);
	u32 bucket = rqsl_hist_bucket_idx(delta_ms);
	atomic64_t *buckets = hist->hist[ctx];

	atomic64_inc(&buckets[bucket]);
	if (!ret)
		atomic64_inc(&hist->success[ctx]);
	else
		atomic64_inc(&hist->failure[ctx]);
}

static int rqspinlock_worker_fn(void *arg)
{
	int cpu = smp_processor_id();
	unsigned long flags;
	u64 start_ns;
	int ret;

	if (cpu) {
		atomic_inc(&rqsl_ready_cpus);

		while (!kthread_should_stop()) {
			struct rqsl_lock_pair locks = rqsl_get_lock_pair(cpu);
			rqspinlock_t *worker_lock = locks.worker_lock;

			if (READ_ONCE(pause)) {
				msleep(1000);
				continue;
			}
			start_ns = ktime_get_mono_fast_ns();
			ret = raw_res_spin_lock_irqsave(worker_lock, flags);
			rqsl_record_lock_result(ktime_get_mono_fast_ns() - start_ns,
						RQSL_CTX_NORMAL, ret);
			mdelay(normal_delay);
			if (!ret)
				raw_res_spin_unlock_irqrestore(worker_lock, flags);
			cpu_relax();
		}
		return 0;
	}

	while (!kthread_should_stop()) {
		int expected = rqsl_nthreads > 0 ? rqsl_nthreads - 1 : 0;
		int ready = atomic_read(&rqsl_ready_cpus);

		if (ready == expected && !READ_ONCE(pause)) {
			for (int i = 0; i < rqsl_nevts; i++)
				perf_event_enable(rqsl_evts[i]);
			pr_err("Waiting 5 secs to pause the test\n");
			msleep(1000 * 5);
			WRITE_ONCE(pause, 1);
			pr_err("Paused the test\n");
		} else {
			msleep(1000);
			cpu_relax();
		}
	}
	return 0;
}

static void nmi_cb(struct perf_event *event, struct perf_sample_data *data,
		   struct pt_regs *regs)
{
	struct rqsl_lock_pair locks;
	int cpu = smp_processor_id();
	unsigned long flags;
	u64 start_ns;
	int ret;

	if (!cpu || READ_ONCE(pause))
		return;

	locks = rqsl_get_lock_pair(cpu);
	start_ns = ktime_get_mono_fast_ns();
	ret = raw_res_spin_lock_irqsave(locks.nmi_lock, flags);
	rqsl_record_lock_result(ktime_get_mono_fast_ns() - start_ns,
				RQSL_CTX_NMI, ret);

	mdelay(nmi_delay);

	if (!ret)
		raw_res_spin_unlock_irqrestore(locks.nmi_lock, flags);
}

static void free_rqsl_threads(void)
{
	int i;

	if (rqsl_threads) {
		for_each_online_cpu(i) {
			if (rqsl_threads[i])
				kthread_stop(rqsl_threads[i]);
		}
		kfree(rqsl_threads);
	}
}

static void free_rqsl_evts(void)
{
	int i;

	if (rqsl_evts) {
		for (i = 0; i < rqsl_nevts; i++) {
			if (rqsl_evts[i])
				perf_event_release_kernel(rqsl_evts[i]);
		}
		kfree(rqsl_evts);
	}
}

static int bpf_test_rqspinlock_init(void)
{
	int i, ret;
	int ncpus = num_online_cpus();

	if (test_mode < RQSL_MODE_AA || test_mode > RQSL_MODE_ABBCCA) {
		pr_err("Invalid mode %d\n", test_mode);
		return -EINVAL;
	}

	pr_err("Mode = %s\n", rqsl_mode_names[test_mode]);

	if (ncpus < test_mode + 2)
		return -ENOTSUPP;

	raw_res_spin_lock_init(&lock_a);
	raw_res_spin_lock_init(&lock_b);
	raw_res_spin_lock_init(&lock_c);

	rqsl_evts = kcalloc(ncpus - 1, sizeof(*rqsl_evts), GFP_KERNEL);
	if (!rqsl_evts)
		return -ENOMEM;
	rqsl_nevts = ncpus - 1;

	for (i = 1; i < ncpus; i++) {
		struct perf_event *e;

		e = perf_event_create_kernel_counter(&hw_attr, i, NULL, nmi_cb, NULL);
		if (IS_ERR(e)) {
			ret = PTR_ERR(e);
			goto err_perf_events;
		}
		rqsl_evts[i - 1] = e;
	}

	rqsl_threads = kcalloc(ncpus, sizeof(*rqsl_threads), GFP_KERNEL);
	if (!rqsl_threads) {
		ret = -ENOMEM;
		goto err_perf_events;
	}
	rqsl_nthreads = ncpus;

	for_each_online_cpu(i) {
		struct task_struct *t;

		t = kthread_create(rqspinlock_worker_fn, NULL, "rqsl_w/%d", i);
		if (IS_ERR(t)) {
			ret = PTR_ERR(t);
			goto err_threads_create;
		}
		kthread_bind(t, i);
		rqsl_threads[i] = t;
		wake_up_process(t);
	}
	return 0;

err_threads_create:
	free_rqsl_threads();
err_perf_events:
	free_rqsl_evts();
	return ret;
}

module_init(bpf_test_rqspinlock_init);

static void rqsl_print_histograms(void)
{
	int cpu, i;

	pr_err("rqspinlock acquisition latency histogram (ms):\n");

	for_each_online_cpu(cpu) {
		struct rqsl_cpu_hist *hist = per_cpu_ptr(&rqsl_cpu_hists, cpu);
		u64 norm_counts[RQSL_NR_HIST_BUCKETS];
		u64 nmi_counts[RQSL_NR_HIST_BUCKETS];
		u64 total_counts[RQSL_NR_HIST_BUCKETS];
		u64 norm_success, nmi_success, success_total;
		u64 norm_failure, nmi_failure, failure_total;
		u64 norm_total = 0, nmi_total = 0, total = 0;
		bool has_slow = false;

		for (i = 0; i < RQSL_NR_HIST_BUCKETS; i++) {
			norm_counts[i] = atomic64_read(&hist->hist[RQSL_CTX_NORMAL][i]);
			nmi_counts[i] = atomic64_read(&hist->hist[RQSL_CTX_NMI][i]);
			total_counts[i] = norm_counts[i] + nmi_counts[i];
			norm_total += norm_counts[i];
			nmi_total += nmi_counts[i];
			total += total_counts[i];
			if (rqsl_hist_ms[i] > RQSL_SLOW_THRESHOLD_MS &&
			    total_counts[i])
				has_slow = true;
		}

		norm_success = atomic64_read(&hist->success[RQSL_CTX_NORMAL]);
		nmi_success = atomic64_read(&hist->success[RQSL_CTX_NMI]);
		norm_failure = atomic64_read(&hist->failure[RQSL_CTX_NORMAL]);
		nmi_failure = atomic64_read(&hist->failure[RQSL_CTX_NMI]);
		success_total = norm_success + nmi_success;
		failure_total = norm_failure + nmi_failure;

		if (!total)
			continue;

		if (!has_slow) {
			pr_err(" cpu%d: total %llu (normal %llu, nmi %llu) | "
			       "success %llu (normal %llu, nmi %llu) | "
			       "failure %llu (normal %llu, nmi %llu), all within 0-%ums\n",
			       cpu, total, norm_total, nmi_total,
			       success_total, norm_success, nmi_success,
			       failure_total, norm_failure, nmi_failure,
			       RQSL_SLOW_THRESHOLD_MS);
			continue;
		}

		pr_err(" cpu%d: total %llu (normal %llu, nmi %llu) | "
		       "success %llu (normal %llu, nmi %llu) | "
		       "failure %llu (normal %llu, nmi %llu)\n",
		       cpu, total, norm_total, nmi_total,
		       success_total, norm_success, nmi_success,
		       failure_total, norm_failure, nmi_failure);
		for (i = 0; i < RQSL_NR_HIST_BUCKETS; i++) {
			unsigned int start_ms;

			if (!total_counts[i])
				continue;

			start_ms = i == 0 ? 0 : rqsl_hist_ms[i - 1] + 1;
			if (i == RQSL_NR_HIST_BUCKETS - 1) {
				pr_err("   >= %ums: total %llu (normal %llu, nmi %llu)\n",
				       start_ms, total_counts[i],
				       norm_counts[i], nmi_counts[i]);
			} else {
				pr_err("   %u-%ums: total %llu (normal %llu, nmi %llu)\n",
				       start_ms, rqsl_hist_ms[i],
				       total_counts[i],
				       norm_counts[i], nmi_counts[i]);
			}
		}
	}
}

static void bpf_test_rqspinlock_exit(void)
{
	WRITE_ONCE(pause, 1);
	free_rqsl_threads();
	free_rqsl_evts();
	rqsl_print_histograms();
}

module_exit(bpf_test_rqspinlock_exit);

MODULE_AUTHOR("Kumar Kartikeya Dwivedi");
MODULE_DESCRIPTION("BPF rqspinlock stress test module");
MODULE_LICENSE("GPL");