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Subject[PATCH] tools/perf: add breakpoint benchmarks
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Add 2 benchmarks:
1. Performance of thread creation/exiting in presence of breakpoints.
2. Performance of breakpoint modification in presence of threads.

The benchmarks capture use cases that we are interested in:
using inheritable breakpoints in large highly-threaded applications.
The benchmarks show significant slowdown imposed by breakpoints
(even when they don't fire).

Testing on Intel 8173M with 112 HW threads show:

perf bench --repeat=56 breakpoint thread --breakpoints=0 --parallelism=56 --threads=20
78.675000 usecs/op
perf bench --repeat=56 breakpoint thread --breakpoints=4 --parallelism=56 --threads=20
12967.135714 usecs/op
That's 165x slowdown due to presence of the breakpoints.

perf bench --repeat=20000 breakpoint enable --passive=0 --active=0
1.433250 usecs/op
perf bench --repeat=20000 breakpoint enable --passive=224 --active=0
585.318400 usecs/op
perf bench --repeat=20000 breakpoint enable --passive=0 --active=111
635.953000 usecs/op
That's 408x and 444x slowdown due to presence of threads.

Profiles show some overhead in toggle_bp_slot,
but also very high contention:

90.83% breakpoint-thre [kernel.kallsyms] [k] osq_lock
4.69% breakpoint-thre [kernel.kallsyms] [k] mutex_spin_on_owner
2.06% breakpoint-thre [kernel.kallsyms] [k] __reserve_bp_slot
2.04% breakpoint-thre [kernel.kallsyms] [k] toggle_bp_slot

79.01% breakpoint-enab [kernel.kallsyms] [k] smp_call_function_single
9.94% breakpoint-enab [kernel.kallsyms] [k] llist_add_batch
5.70% breakpoint-enab [kernel.kallsyms] [k] _raw_spin_lock_irq
1.84% breakpoint-enab [kernel.kallsyms] [k] event_function_call
1.12% breakpoint-enab [kernel.kallsyms] [k] send_call_function_single_ipi
0.37% breakpoint-enab [kernel.kallsyms] [k] generic_exec_single
0.24% breakpoint-enab [kernel.kallsyms] [k] __perf_event_disable
0.20% breakpoint-enab [kernel.kallsyms] [k] _perf_event_enable
0.18% breakpoint-enab [kernel.kallsyms] [k] toggle_bp_slot

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: linux-perf-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
tools/perf/bench/Build | 1 +
tools/perf/bench/bench.h | 2 +
tools/perf/bench/breakpoint.c | 235 ++++++++++++++++++++++++++++++++++
tools/perf/builtin-bench.c | 8 ++
4 files changed, 246 insertions(+)
create mode 100644 tools/perf/bench/breakpoint.c

diff --git a/tools/perf/bench/Build b/tools/perf/bench/Build
index 61d45fcb4057c..6b6155a8ad096 100644
--- a/tools/perf/bench/Build
+++ b/tools/perf/bench/Build
@@ -14,6 +14,7 @@ perf-y += kallsyms-parse.o
perf-y += find-bit-bench.o
perf-y += inject-buildid.o
perf-y += evlist-open-close.o
+perf-y += breakpoint.o

perf-$(CONFIG_X86_64) += mem-memcpy-x86-64-asm.o
perf-$(CONFIG_X86_64) += mem-memset-x86-64-asm.o
diff --git a/tools/perf/bench/bench.h b/tools/perf/bench/bench.h
index b3480bc33fe84..6cefb4315d75e 100644
--- a/tools/perf/bench/bench.h
+++ b/tools/perf/bench/bench.h
@@ -49,6 +49,8 @@ int bench_synthesize(int argc, const char **argv);
int bench_kallsyms_parse(int argc, const char **argv);
int bench_inject_build_id(int argc, const char **argv);
int bench_evlist_open_close(int argc, const char **argv);
+int bench_breakpoint_thread(int argc, const char **argv);
+int bench_breakpoint_enable(int argc, const char **argv);

#define BENCH_FORMAT_DEFAULT_STR "default"
#define BENCH_FORMAT_DEFAULT 0
diff --git a/tools/perf/bench/breakpoint.c b/tools/perf/bench/breakpoint.c
new file mode 100644
index 0000000000000..56936fea246d7
--- /dev/null
+++ b/tools/perf/bench/breakpoint.c
@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <subcmd/parse-options.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/perf_event.h>
+#include <linux/time64.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <sys/time.h>
+#include <pthread.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include "bench.h"
+#include "futex.h"
+
+struct {
+ unsigned int nbreakpoints;
+ unsigned int nparallel;
+ unsigned int nthreads;
+} thread_params = {
+ .nbreakpoints = 1,
+ .nparallel = 1,
+ .nthreads = 1,
+};
+
+static const struct option thread_options[] = {
+ OPT_UINTEGER('b', "breakpoints", &thread_params.nbreakpoints,
+ "Specify amount of breakpoints"),
+ OPT_UINTEGER('p', "parallelism", &thread_params.nparallel, "Specify amount of parallelism"),
+ OPT_UINTEGER('t', "threads", &thread_params.nthreads, "Specify amount of threads"),
+ OPT_END()
+};
+
+static const char * const thread_usage[] = {
+ "perf bench breakpoint thread <options>",
+ NULL
+};
+
+struct breakpoint {
+ int fd;
+ char watched;
+};
+
+static int breakpoint_setup(void *addr)
+{
+ struct perf_event_attr attr = {0};
+
+ attr.type = PERF_TYPE_BREAKPOINT;
+ attr.size = sizeof(attr);
+ attr.inherit = 1;
+ attr.exclude_kernel = 1;
+ attr.exclude_hv = 1;
+ attr.bp_addr = (uint64_t)addr;
+ attr.bp_type = HW_BREAKPOINT_RW;
+ attr.bp_len = HW_BREAKPOINT_LEN_1;
+ return syscall(SYS_perf_event_open, &attr, 0, -1, -1, 0);
+}
+
+static void *passive_thread(void *arg)
+{
+ unsigned int *done = (unsigned int *)arg;
+
+ while (!__atomic_load_n(done, __ATOMIC_RELAXED))
+ futex_wait(done, 0, NULL, 0);
+ return NULL;
+}
+
+static void *active_thread(void *arg)
+{
+ unsigned int *done = (unsigned int *)arg;
+
+ while (!__atomic_load_n(done, __ATOMIC_RELAXED));
+ return NULL;
+}
+
+static void *breakpoint_thread(void *arg)
+{
+ unsigned int i, done;
+ int *repeat = (int *)arg;
+ pthread_t *threads;
+
+ threads = calloc(thread_params.nthreads, sizeof(threads[0]));
+ while (__atomic_fetch_sub(repeat, 1, __ATOMIC_RELAXED) > 0) {
+ done = 0;
+ for (i = 0; i < thread_params.nthreads; i++) {
+ if (pthread_create(&threads[i], NULL, passive_thread, &done))
+ exit((perror("pthread_create"), EXIT_FAILURE));
+ }
+ __atomic_store_n(&done, 1, __ATOMIC_RELAXED);
+ futex_wake(&done, thread_params.nthreads, 0);
+ for (i = 0; i < thread_params.nthreads; i++)
+ pthread_join(threads[i], NULL);
+ }
+ free(threads);
+ return NULL;
+}
+
+// The benchmark creates nbreakpoints inheritable breakpoints,
+// then starts nparallel threads which create and join bench_repeat batches of nthreads threads.
+int bench_breakpoint_thread(int argc, const char **argv)
+{
+ unsigned int i, result_usec;
+ int repeat = bench_repeat;
+ struct breakpoint *breakpoints;
+ pthread_t *parallel;
+ struct timeval start, stop, diff;
+
+ if (parse_options(argc, argv, thread_options, thread_usage, 0)) {
+ usage_with_options(thread_usage, thread_options);
+ exit(EXIT_FAILURE);
+ }
+ breakpoints = calloc(thread_params.nbreakpoints, sizeof(breakpoints[0]));
+ parallel = calloc(thread_params.nparallel, sizeof(parallel[0]));
+ for (i = 0; i < thread_params.nbreakpoints; i++) {
+ breakpoints[i].fd = breakpoint_setup(&breakpoints[i].watched);
+ if (breakpoints[i].fd == -1)
+ exit((perror("perf_event_open"), EXIT_FAILURE));
+ }
+ gettimeofday(&start, NULL);
+ for (i = 0; i < thread_params.nparallel; i++) {
+ if (pthread_create(&parallel[i], NULL, breakpoint_thread, &repeat))
+ exit((perror("pthread_create"), EXIT_FAILURE));
+ }
+ for (i = 0; i < thread_params.nparallel; i++)
+ pthread_join(parallel[i], NULL);
+ gettimeofday(&stop, NULL);
+ timersub(&stop, &start, &diff);
+ for (i = 0; i < thread_params.nbreakpoints; i++)
+ close(breakpoints[i].fd);
+ free(parallel);
+ free(breakpoints);
+ switch (bench_format) {
+ case BENCH_FORMAT_DEFAULT:
+ printf("# Created/joined %d threads with %d breakpoints and %d parallelism\n",
+ bench_repeat, thread_params.nbreakpoints, thread_params.nparallel);
+ printf(" %14s: %lu.%03lu [sec]\n\n", "Total time",
+ (long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+ result_usec = diff.tv_sec * USEC_PER_SEC + diff.tv_usec;
+ printf(" %14lf usecs/op\n",
+ (double)result_usec / bench_repeat / thread_params.nthreads);
+ printf(" %14lf usecs/op/cpu\n",
+ (double)result_usec / bench_repeat /
+ thread_params.nthreads * thread_params.nparallel);
+ break;
+ case BENCH_FORMAT_SIMPLE:
+ printf("%lu.%03lu\n", (long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+ break;
+ default:
+ fprintf(stderr, "Unknown format: %d\n", bench_format);
+ exit(EXIT_FAILURE);
+ }
+ return 0;
+}
+
+struct {
+ unsigned int npassive;
+ unsigned int nactive;
+} enable_params = {
+ .nactive = 0,
+ .npassive = 0,
+};
+
+static const struct option enable_options[] = {
+ OPT_UINTEGER('p', "passive", &enable_params.npassive, "Specify amount of passive threads"),
+ OPT_UINTEGER('a', "active", &enable_params.nactive, "Specify amount of active threads"),
+ OPT_END()
+};
+
+static const char * const enable_usage[] = {
+ "perf bench breakpoint enable <options>",
+ NULL
+};
+
+// The benchmark creates an inheritable breakpoint,
+// then starts npassive threads that block and nactive threads that actively spin
+// and then disables and enables the breakpoint bench_repeat times.
+int bench_breakpoint_enable(int argc, const char **argv)
+{
+ unsigned int i, nthreads, result_usec, done = 0;
+ char watched;
+ int fd;
+ pthread_t *threads;
+ struct timeval start, stop, diff;
+
+ if (parse_options(argc, argv, enable_options, enable_usage, 0)) {
+ usage_with_options(enable_usage, enable_options);
+ exit(EXIT_FAILURE);
+ }
+ fd = breakpoint_setup(&watched);
+ if (fd == -1)
+ exit((perror("perf_event_open"), EXIT_FAILURE));
+ nthreads = enable_params.npassive + enable_params.nactive;
+ threads = calloc(nthreads, sizeof(threads[0]));
+ for (i = 0; i < nthreads; i++) {
+ if (pthread_create(&threads[i], NULL,
+ i < enable_params.npassive ? passive_thread : active_thread, &done))
+ exit((perror("pthread_create"), EXIT_FAILURE));
+ }
+ usleep(10000); // let the threads block
+ gettimeofday(&start, NULL);
+ for (i = 0; i < bench_repeat; i++) {
+ if (ioctl(fd, PERF_EVENT_IOC_DISABLE, 0))
+ exit((perror("ioctl(PERF_EVENT_IOC_DISABLE)"), EXIT_FAILURE));
+ if (ioctl(fd, PERF_EVENT_IOC_ENABLE, 0))
+ exit((perror("ioctl(PERF_EVENT_IOC_ENABLE)"), EXIT_FAILURE));
+ }
+ gettimeofday(&stop, NULL);
+ timersub(&stop, &start, &diff);
+ __atomic_store_n(&done, 1, __ATOMIC_RELAXED);
+ futex_wake(&done, enable_params.npassive, 0);
+ for (i = 0; i < nthreads; i++)
+ pthread_join(threads[i], NULL);
+ free(threads);
+ close(fd);
+ switch (bench_format) {
+ case BENCH_FORMAT_DEFAULT:
+ printf("# Enabled/disabled breakpoint %d time with %d passive and %d active threads\n",
+ bench_repeat, enable_params.npassive, enable_params.nactive);
+ printf(" %14s: %lu.%03lu [sec]\n\n", "Total time",
+ (long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+ result_usec = diff.tv_sec * USEC_PER_SEC + diff.tv_usec;
+ printf(" %14lf usecs/op\n", (double)result_usec / bench_repeat);
+ break;
+ case BENCH_FORMAT_SIMPLE:
+ printf("%lu.%03lu\n", (long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+ break;
+ default:
+ fprintf(stderr, "Unknown format: %d\n", bench_format);
+ exit(EXIT_FAILURE);
+ }
+ return 0;
+}
diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index d291f3a8af5f2..334ab897aae3b 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -92,6 +92,13 @@ static struct bench internals_benchmarks[] = {
{ NULL, NULL, NULL }
};

+static struct bench breakpoint_benchmarks[] = {
+ { "thread", "Benchmark thread start/finish with breakpoints", bench_breakpoint_thread},
+ { "enable", "Benchmark breakpoint enable/disable", bench_breakpoint_enable},
+ { "all", "Run all breakpoint benchmarks", NULL},
+ { NULL, NULL, NULL },
+};
+
struct collection {
const char *name;
const char *summary;
@@ -110,6 +117,7 @@ static struct collection collections[] = {
{"epoll", "Epoll stressing benchmarks", epoll_benchmarks },
#endif
{ "internals", "Perf-internals benchmarks", internals_benchmarks },
+ { "breakpoint", "Breakpoint benchmarks", breakpoint_benchmarks },
{ "all", "All benchmarks", NULL },
{ NULL, NULL, NULL }
};
base-commit: bd24325684029a48f20a188b899eb84900d0bc9c
--
2.36.0.464.gb9c8b46e94-goog

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