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Message-ID: <aIr8JuprT1JPNJsq@google.com>
Date: Wed, 30 Jul 2025 22:16:22 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Yuzhuo Jing <yuzhuo@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Liang Kan <kan.liang@...ux.intel.com>, Yuzhuo Jing <yzj@...ch.edu>,
Andrea Parri <parri.andrea@...il.com>,
Palmer Dabbelt <palmer@...osinc.com>,
Charlie Jenkins <charlie@...osinc.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Kumar Kartikeya Dwivedi <memxor@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Barret Rhoden <brho@...gle.com>,
Alexandre Ghiti <alexghiti@...osinc.com>,
Guo Ren <guoren@...nel.org>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v1 6/7] perf bench: Add 'bench sync qspinlock' subcommand
On Mon, Jul 28, 2025 at 07:26:39PM -0700, Yuzhuo Jing wrote:
> Benchmark kernel queued spinlock implementation in user space. Support
> settings of the number of threads and the number of acquire/releases.
My general advice is that you'd better add an example command line and
output in the commit message if you add any user-visible changes. Also
please update the Documentation/perf-bench.txt.
Thanks,
Namhyung
>
> Signed-off-by: Yuzhuo Jing <yuzhuo@...gle.com>
> ---
> tools/perf/bench/Build | 2 +
> tools/perf/bench/bench.h | 1 +
> tools/perf/bench/sync.c | 234 +++++++++++++++++++++++++++++++++++++
> tools/perf/builtin-bench.c | 7 ++
> 4 files changed, 244 insertions(+)
> create mode 100644 tools/perf/bench/sync.c
>
> diff --git a/tools/perf/bench/Build b/tools/perf/bench/Build
> index b558ab98719f..13558279fa0e 100644
> --- a/tools/perf/bench/Build
> +++ b/tools/perf/bench/Build
> @@ -19,6 +19,8 @@ perf-bench-y += evlist-open-close.o
> perf-bench-y += breakpoint.o
> perf-bench-y += pmu-scan.o
> perf-bench-y += uprobe.o
> +perf-bench-y += sync.o
> +perf-bench-y += qspinlock.o
>
> perf-bench-$(CONFIG_X86_64) += mem-memcpy-x86-64-asm.o
> perf-bench-$(CONFIG_X86_64) += mem-memset-x86-64-asm.o
> diff --git a/tools/perf/bench/bench.h b/tools/perf/bench/bench.h
> index 9f736423af53..dd6c8b6126d3 100644
> --- a/tools/perf/bench/bench.h
> +++ b/tools/perf/bench/bench.h
> @@ -22,6 +22,7 @@ int bench_numa(int argc, const char **argv);
> int bench_sched_messaging(int argc, const char **argv);
> int bench_sched_pipe(int argc, const char **argv);
> int bench_sched_seccomp_notify(int argc, const char **argv);
> +int bench_sync_qspinlock(int argc, const char **argv);
> int bench_syscall_basic(int argc, const char **argv);
> int bench_syscall_getpgid(int argc, const char **argv);
> int bench_syscall_fork(int argc, const char **argv);
> diff --git a/tools/perf/bench/sync.c b/tools/perf/bench/sync.c
> new file mode 100644
> index 000000000000..2685cb66584c
> --- /dev/null
> +++ b/tools/perf/bench/sync.c
> @@ -0,0 +1,234 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Synchronization benchmark.
> + *
> + * 2025 Yuzhuo Jing <yuzhuo@...gle.com>
> + */
> +#include <bits/time.h>
> +#include <err.h>
> +#include <inttypes.h>
> +#include <perf/cpumap.h>
> +#include <pthread.h>
> +#include <stdbool.h>
> +#include <string.h>
> +#include <subcmd/parse-options.h>
> +#include <sys/cdefs.h>
> +
> +#include "bench.h"
> +
> +#include "include/qspinlock.h"
> +
> +#define NS 1000000000ull
> +#define CACHELINE_SIZE 64
> +
> +static unsigned int nthreads;
> +static unsigned long nspins = 10000ul;
> +
> +struct barrier_t;
> +
> +typedef void(*lock_fn)(void *);
> +
> +/*
> + * Lock operation definition to support multiple implmentations of locks.
> + *
> + * The lock and unlock functions only take one variable, the data pointer.
> + */
> +struct lock_ops {
> + lock_fn lock;
> + lock_fn unlock;
> + void *data;
> +};
> +
> +struct worker {
> + pthread_t thd;
> + unsigned int tid;
> + struct lock_ops *ops;
> + struct barrier_t *barrier;
> + u64 runtime; // in nanoseconds
> +};
> +
> +static const struct option options[] = {
> + OPT_UINTEGER('t', "threads", &nthreads,
> + "Specify number of threads (default: number of CPUs)."),
> + OPT_ULONG('n', "spins", &nspins,
> + "Number of lock acquire operations per thread (default: 10,000 times)."),
> + OPT_END()
> +};
> +
> +static const char *const bench_sync_usage[] = {
> + "perf bench sync qspinlock <options>",
> + NULL
> +};
> +
> +/*
> + * A atomic-based barrier. Expect to have lower latency than pthread barrier
> + * that sleeps the thread.
> + */
> +struct barrier_t {
> + unsigned int count __aligned(CACHELINE_SIZE);
> +};
> +
> +/*
> + * A atomic-based barrier. Expect to have lower latency than pthread barrier
> + * that sleeps the thread.
> + */
> +__always_inline void wait_barrier(struct barrier_t *b)
> +{
> + if (__atomic_sub_fetch(&b->count, 1, __ATOMIC_RELAXED) == 0)
> + return;
> + while (__atomic_load_n(&b->count, __ATOMIC_RELAXED))
> + ;
> +}
> +
> +static int bench_sync_lock_generic(struct lock_ops *ops, int argc, const char **argv);
> +
> +/*
> + * Benchmark of linux kernel queued spinlock in user land.
> + */
> +int bench_sync_qspinlock(int argc, const char **argv)
> +{
> + struct qspinlock lock = __ARCH_SPIN_LOCK_UNLOCKED;
> + struct lock_ops ops = {
> + .lock = (lock_fn)queued_spin_lock,
> + .unlock = (lock_fn)queued_spin_unlock,
> + .data = &lock,
> + };
> + return bench_sync_lock_generic(&ops, argc, argv);
> +}
> +
> +/*
> + * A busy loop to acquire and release the given lock N times.
> + */
> +static void lock_loop(const struct lock_ops *ops, unsigned long n)
> +{
> + unsigned long i;
> +
> + for (i = 0; i < n; ++i) {
> + ops->lock(ops->data);
> + ops->unlock(ops->data);
> + }
> +}
> +
> +/*
> + * Thread worker function. Runs lock loop for N/5 times before and after
> + * the main timed loop.
> + */
> +static void *sync_workerfn(void *args)
> +{
> + struct worker *worker = (struct worker *)args;
> + struct timespec starttime, endtime;
> +
> + set_this_cpu_id(worker->tid);
> +
> + /* Barrier to let all threads start together */
> + wait_barrier(worker->barrier);
> +
> + /* Warmup loop (not counted) to keep the below loop contended. */
> + lock_loop(worker->ops, nspins / 5);
> +
> + clock_gettime(CLOCK_THREAD_CPUTIME_ID, &starttime);
> + lock_loop(worker->ops, nspins);
> + clock_gettime(CLOCK_THREAD_CPUTIME_ID, &endtime);
> +
> + /* Tail loop (not counted) to keep the above loop contended. */
> + lock_loop(worker->ops, nspins / 5);
> +
> + worker->runtime = (endtime.tv_sec - starttime.tv_sec) * NS
> + + endtime.tv_nsec - starttime.tv_nsec;
> +
> + return NULL;
> +}
> +
> +/*
> + * Generic lock synchronization benchmark function. Sets up threads and
> + * thread affinities.
> + */
> +static int bench_sync_lock_generic(struct lock_ops *ops, int argc, const char **argv)
> +{
> + struct perf_cpu_map *online_cpus;
> + unsigned int online_cpus_nr;
> + struct worker *workers;
> + u64 totaltime = 0, total_spins, avg_ns, avg_ns_dot;
> + struct barrier_t barrier;
> + cpu_set_t *cpuset;
> + size_t cpuset_size;
> +
> + argc = parse_options(argc, argv, options, bench_sync_usage, 0);
> + if (argc) {
> + usage_with_options(bench_sync_usage, options);
> + exit(EXIT_FAILURE);
> + }
> +
> + /* CPU count setup. */
> + online_cpus = perf_cpu_map__new_online_cpus();
> + if (!online_cpus)
> + err(EXIT_FAILURE, "No online CPUs available");
> + online_cpus_nr = perf_cpu_map__nr(online_cpus);
> +
> + if (!nthreads) /* default to the number of CPUs */
> + nthreads = online_cpus_nr;
> +
> + workers = calloc(nthreads, sizeof(*workers));
> + if (!workers)
> + err(EXIT_FAILURE, "calloc");
> +
> + barrier.count = nthreads;
> +
> + printf("Running with %u threads.\n", nthreads);
> +
> + cpuset = CPU_ALLOC(online_cpus_nr);
> + if (!cpuset)
> + err(EXIT_FAILURE, "Cannot allocate cpuset.");
> + cpuset_size = CPU_ALLOC_SIZE(online_cpus_nr);
> +
> + /* Create worker data structures, set CPU affinity, and create */
> + for (unsigned int i = 0; i < nthreads; ++i) {
> + pthread_attr_t thread_attr;
> + int ret;
> +
> + /* Basic worker thread information */
> + workers[i].tid = i;
> + workers[i].barrier = &barrier;
> + workers[i].ops = ops;
> +
> + /* Set CPU affinity */
> + pthread_attr_init(&thread_attr);
> + CPU_ZERO_S(cpuset_size, cpuset);
> + CPU_SET_S(perf_cpu_map__cpu(online_cpus, i % online_cpus_nr).cpu,
> + cpuset_size, cpuset);
> +
> + if (pthread_attr_setaffinity_np(&thread_attr, cpuset_size, cpuset))
> + err(EXIT_FAILURE, "Pthread set affinity failed");
> +
> + /* Create and block thread */
> + ret = pthread_create(&workers[i].thd, &thread_attr, sync_workerfn, &workers[i]);
> + if (ret != 0)
> + err(EXIT_FAILURE, "Error creating thread: %s", strerror(ret));
> +
> + pthread_attr_destroy(&thread_attr);
> + }
> +
> + CPU_FREE(cpuset);
> +
> + for (unsigned int i = 0; i < nthreads; ++i) {
> + int ret = pthread_join(workers[i].thd, NULL);
> +
> + if (ret)
> + err(EXIT_FAILURE, "pthread_join");
> + }
> +
> + /* Calculate overall average latency. */
> + for (unsigned int i = 0; i < nthreads; ++i)
> + totaltime += workers[i].runtime;
> +
> + total_spins = (u64)nthreads * nspins;
> + avg_ns = totaltime / total_spins;
> + avg_ns_dot = (totaltime % total_spins) * 10000 / total_spins;
> +
> + printf("Lock-unlock latency of %u threads: %"PRIu64".%"PRIu64" ns.\n",
> + nthreads, avg_ns, avg_ns_dot);
> +
> + free(workers);
> +
> + return 0;
> +}
> diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
> index 2c1a9f3d847a..cfe6f6dc6ed4 100644
> --- a/tools/perf/builtin-bench.c
> +++ b/tools/perf/builtin-bench.c
> @@ -52,6 +52,12 @@ static struct bench sched_benchmarks[] = {
> { NULL, NULL, NULL }
> };
>
> +static struct bench sync_benchmarks[] = {
> + { "qspinlock", "Benchmark for queued spinlock", bench_sync_qspinlock },
> + { "all", "Run all synchronization benchmarks", NULL },
> + { NULL, NULL, NULL }
> +};
> +
> static struct bench syscall_benchmarks[] = {
> { "basic", "Benchmark for basic getppid(2) calls", bench_syscall_basic },
> { "getpgid", "Benchmark for getpgid(2) calls", bench_syscall_getpgid },
> @@ -122,6 +128,7 @@ struct collection {
>
> static struct collection collections[] = {
> { "sched", "Scheduler and IPC benchmarks", sched_benchmarks },
> + { "sync", "Synchronization benchmarks", sync_benchmarks },
> { "syscall", "System call benchmarks", syscall_benchmarks },
> { "mem", "Memory access benchmarks", mem_benchmarks },
> #ifdef HAVE_LIBNUMA_SUPPORT
> --
> 2.50.1.487.gc89ff58d15-goog
>
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