From: Peter Oskolkov <p...@google.com>
This is the final RFC patch in FUTEX_SWAP patchset. It
adds a test/benchmark to validate behavior and
compare performance of a new FUTEX_SWAP futex operation.
Detailed API design and behavior considerations are provided
in the commit messages of the previous two patches.
Signed-off-by: Peter Oskolkov <p...@google.com>
---
.../selftests/futex/functional/.gitignore | 1 +
.../selftests/futex/functional/Makefile | 1 +
.../selftests/futex/functional/futex_swap.c | 209 ++++++++++++++++++
.../selftests/futex/include/futextest.h | 19 ++
4 files changed, 230 insertions(+)
create mode 100644 tools/testing/selftests/futex/functional/futex_swap.c
diff --git a/tools/testing/selftests/futex/functional/.gitignore
b/tools/testing/selftests/futex/functional/.gitignore
index 0efcd494daab..d661ef0946cc 100644
--- a/tools/testing/selftests/futex/functional/.gitignore
+++ b/tools/testing/selftests/futex/functional/.gitignore
@@ -2,6 +2,7 @@
futex_requeue_pi
futex_requeue_pi_mismatched_ops
futex_requeue_pi_signal_restart
+futex_swap
futex_wait_private_mapped_file
futex_wait_timeout
futex_wait_uninitialized_heap
diff --git a/tools/testing/selftests/futex/functional/Makefile
b/tools/testing/selftests/futex/functional/Makefile
index 23207829ec75..6992fac38b15 100644
--- a/tools/testing/selftests/futex/functional/Makefile
+++ b/tools/testing/selftests/futex/functional/Makefile
@@ -13,6 +13,7 @@ TEST_GEN_FILES := \
futex_requeue_pi \
futex_requeue_pi_signal_restart \
futex_requeue_pi_mismatched_ops \
+ futex_swap \
futex_wait_uninitialized_heap \
futex_wait_private_mapped_file
diff --git a/tools/testing/selftests/futex/functional/futex_swap.c
b/tools/testing/selftests/futex/functional/futex_swap.c
new file mode 100644
index 000000000000..9034d04372d3
--- /dev/null
+++ b/tools/testing/selftests/futex/functional/futex_swap.c
@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <errno.h>
+#include <getopt.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include "atomic.h"
+#include "futextest.h"
+
+/* The futex the main thread waits on. */
+futex_t futex_main = FUTEX_INITIALIZER;
+/* The futex the other thread wats on. */
+futex_t futex_other = FUTEX_INITIALIZER;
+
+/* The number of iterations to run (>1 => run benchmarks. */
+static int cfg_iterations = 1;
+
+/* If != 0, print diagnostic messages. */
+static int cfg_verbose;
+
+/* If == 0, do not use validation_counter. Useful for benchmarking. */
+static int cfg_validate = 1;
+
+/* How to swap threads. */
+#define SWAP_WAKE_WAIT 1
+#define SWAP_SWAP 2
+
+/* Futex values. */
+#define FUTEX_WAITING 0
+#define FUTEX_WAKEUP 1
+
+/* An atomic counter used to validate proper swapping. */
+static atomic_t validation_counter;
+
+void futex_swap_op(int mode, futex_t *futex_this, futex_t *futex_that)
+{
+ int ret;
+
+ switch (mode) {
+ case SWAP_WAKE_WAIT:
+ futex_set(futex_this, FUTEX_WAITING);
+ futex_set(futex_that, FUTEX_WAKEUP);
+ futex_wake(futex_that, 1, FUTEX_PRIVATE_FLAG);
+ futex_wait(futex_this, FUTEX_WAITING, NULL, FUTEX_PRIVATE_FLAG);
+ if (*futex_this != FUTEX_WAKEUP) {
+ fprintf(stderr, "unexpected futex_this value on
wakeup\n");
+ exit(1);
+ }
+ break;
+
+ case SWAP_SWAP:
+ futex_set(futex_this, FUTEX_WAITING);
+ futex_set(futex_that, FUTEX_WAKEUP);
+ ret = futex_swap(futex_this, FUTEX_WAITING, NULL,
+ futex_that, FUTEX_PRIVATE_FLAG);
+ if (ret < 0 && errno == ENOSYS) {
+ /* futex_swap not implemented */
+ perror("futex_swap");
+ exit(1);
+ }
+ if (*futex_this != FUTEX_WAKEUP) {
+ fprintf(stderr, "unexpected futex_this value on
wakeup\n");
+ exit(1);
+ }
+ break;
+
+ default:
+ fprintf(stderr, "unknown mode in %s\n", __func__);
+ exit(1);
+ }
+}
+
+void *other_thread(void *arg)
+{
+ int mode = *((int *)arg);
+ int counter;
+
+ if (cfg_verbose)
+ printf("%s started\n", __func__);
+
+ futex_wait(&futex_other, 0, NULL, FUTEX_PRIVATE_FLAG);
+
+ for (counter = 0; counter < cfg_iterations; ++counter) {
+ if (cfg_validate) {
+ int prev = 2 * counter + 1;
+
+ if (prev != atomic_cmpxchg(&validation_counter, prev,
+ prev + 1)) {
+ fprintf(stderr, "swap validation failed\n");
+ exit(1);
+ }
+ }
+ futex_swap_op(mode, &futex_other, &futex_main);
+ }
+
+ if (cfg_verbose)
+ printf("%s finished: %d iteration(s)\n", __func__, counter);
+
+ return NULL;
+}
+
+void run_test(int mode)
+{
+ struct timespec start, stop;
+ int ret, counter;
+ pthread_t thread;
+ uint64_t duration;
+
+ futex_set(&futex_other, FUTEX_WAITING);
+ atomic_set(&validation_counter, 0);
+ ret = pthread_create(&thread, NULL, &other_thread, &mode);
+ if (ret) {
+ perror("pthread_create");
+ exit(1);
+ }
+
+ ret = clock_gettime(CLOCK_MONOTONIC, &start);
+ if (ret) {
+ perror("clock_gettime");
+ exit(1);
+ }
+
+ for (counter = 0; counter < cfg_iterations; ++counter) {
+ if (cfg_validate) {
+ int prev = 2 * counter;
+
+ if (prev != atomic_cmpxchg(&validation_counter, prev,
+ prev + 1)) {
+ fprintf(stderr, "swap validation failed\n");
+ exit(1);
+ }
+ }
+ futex_swap_op(mode, &futex_main, &futex_other);
+ }
+ if (cfg_validate && validation_counter.val != 2 * cfg_iterations) {
+ fprintf(stderr, "final swap validation failed\n");
+ exit(1);
+ }
+
+ ret = clock_gettime(CLOCK_MONOTONIC, &stop);
+ if (ret) {
+ perror("clock_gettime");
+ exit(1);
+ }
+
+ duration = (stop.tv_sec - start.tv_sec) * 1000000000LL +
+ stop.tv_nsec - start.tv_nsec;
+ if (cfg_verbose || cfg_iterations > 1) {
+ printf("completed %d swap and back iterations in %lu ns: %lu ns
per swap\n",
+ cfg_iterations, duration,
+ duration / (cfg_iterations * 2));
+ }
+
+ /* The remote thread is blocked; send it the final wake. */
+ futex_set(&futex_other, FUTEX_WAKEUP);
+ futex_wake(&futex_other, 1, FUTEX_PRIVATE_FLAG);
+ if (pthread_join(thread, NULL)) {
+ perror("pthread_join");
+ exit(1);
+ }
+}
+
+void usage(char *prog)
+{
+ printf("Usage: %s\n", prog);
+ printf(" -h Display this help message\n");
+ printf(" -i N Use N iterations to benchmark\n");
+ printf(" -n Do not validate swapping correctness\n");
+ printf(" -v Print diagnostic messages\n");
+}
+
+int main(int argc, char *argv[])
+{
+ int c;
+
+ while ((c = getopt(argc, argv, "hi:nv")) != -1) {
+ switch (c) {
+ case 'h':
+ usage(basename(argv[0]));
+ exit(0);
+ case 'i':
+ cfg_iterations = atoi(optarg);
+ break;
+ case 'n':
+ cfg_validate = 0;
+ break;
+ case 'v':
+ cfg_verbose = 1;
+ break;
+ default:
+ usage(basename(argv[0]));
+ exit(1);
+ }
+ }
+
+ printf("\n\n------- running SWAP_WAKE_WAIT -----------\n\n");
+ run_test(SWAP_WAKE_WAIT);
+ printf("PASS\n");
+
+ printf("\n\n------- running SWAP_SWAP -----------\n\n");
+ run_test(SWAP_SWAP);
+ printf("PASS\n");
+
+ return 0;
+}
diff --git a/tools/testing/selftests/futex/include/futextest.h
b/tools/testing/selftests/futex/include/futextest.h
index ddbcfc9b7bac..4d6a0a18445a 100644
--- a/tools/testing/selftests/futex/include/futextest.h
+++ b/tools/testing/selftests/futex/include/futextest.h
@@ -38,6 +38,9 @@ typedef volatile u_int32_t futex_t;
#ifndef FUTEX_CMP_REQUEUE_PI
#define FUTEX_CMP_REQUEUE_PI 12
#endif
+#ifndef FUTEX_SWAP
+#define FUTEX_SWAP 13
+#endif
#ifndef FUTEX_WAIT_REQUEUE_PI_PRIVATE
#define FUTEX_WAIT_REQUEUE_PI_PRIVATE (FUTEX_WAIT_REQUEUE_PI | \
FUTEX_PRIVATE_FLAG)
@@ -46,6 +49,9 @@ typedef volatile u_int32_t futex_t;
#define FUTEX_CMP_REQUEUE_PI_PRIVATE (FUTEX_CMP_REQUEUE_PI | \
FUTEX_PRIVATE_FLAG)
#endif
+#ifndef FUTEX_SWAP_PRIVATE
+#define FUTEX_SWAP_PRIVATE (FUTEX_WAIT_WAKE | FUTEX_PRIVATE_FLAG)
+#endif
/**
* futex() - SYS_futex syscall wrapper
@@ -204,6 +210,19 @@ futex_cmp_requeue_pi(futex_t *uaddr, futex_t val, futex_t
*uaddr2, int nr_wake,
val, opflags);
}
+/**
+ * futex_swap() - block on uaddr and wake one task blocked on uaddr2.
+ * @uaddr: futex to block the current task on
+ * @timeout: relative timeout for the current task block
+ * @uaddr2: futex to wake tasks at (can be the same as uaddr)
+ */
+static inline int
+futex_swap(futex_t *uaddr, futex_t val, struct timespec *timeout,
+ futex_t *uaddr2, int opflags)
+{
+ return futex(uaddr, FUTEX_SWAP, val, timeout, uaddr2, 0, opflags);
+}
+
/**
* futex_cmpxchg() - atomic compare and exchange
* @uaddr: The address of the futex to be modified
--
2.25.1
