Re: [PATCH] futex: add FUTEX_SET_WAIT operation

Darren Hart
2009-11-19T17:04:09Z

Michel Lespinasse wrote:
> On Tue, Nov 17, 2009 at 08:16:06AM -0800, Darren Hart wrote:
>>> http://git.kernel.org/?p=linux/kernel/git/dvhart/futextest.git
>> Michael, would you be willing to include a version of this test in the
>> above test suite? If so, then in keeping with the rest of the test suite,
>> I would recommend splitting into two tests, one of each opcode being
>> tested, and add argument to define thread count. The run.sh script would
>> then run each thread count as a separate test run.
>
> There you go. Hope this helps. Feel free to adapt as needed.
>
> Signed-off-by: Michel Lespinasse <walken@google.com>

My core-duo laptop hung after 256 threads. I left it running all night
and woke to it still sitting at:

256 threads: 11792 Kiter/s (14.18s user 0.28s system 8.48s wall 1.71 cores)

Have experienced a hang with this test on any platform? I'll take a
closer look at the source today to see if there is anything in there
that requires a certain number of CPUs to function properly.

--
Darren

>
> diff --git a/functional/futex_requeue_pi_mismatched_ops.c b/functional/futex_requeue_pi_mismatched_ops.c
> index 50bd07b..529f5a8 100644
> --- a/functional/futex_requeue_pi_mismatched_ops.c
> +++ b/functional/futex_requeue_pi_mismatched_ops.c
> @@ -113,7 +113,7 @@ int main(int argc, char *argv[])
> * requeue_pi target and aborted. Wake the child with
> * FUTEX_WAKE.
> */
> - ret = futex_wake(&f1, f1, 1, FUTEX_PRIVATE_FLAG);
> + ret = futex_wake(&f1, 1, FUTEX_PRIVATE_FLAG);
> if (ret == 1)
> ret = 0;
> else if (ret < 0)
> diff --git a/include/futextest.h b/include/futextest.h
> index 2b64f79..853c3c4 100644
> --- a/include/futextest.h
> +++ b/include/futextest.h
> @@ -78,6 +78,9 @@ int _verbose = VCRITICAL;
> #ifndef FUTEX_CMP_REQUEUE_PI
> #define FUTEX_CMP_REQUEUE_PI 12
> #endif
> +#ifndef FUTEX_SET_WAIT
> +#define FUTEX_SET_WAIT 13
> +#endif
> #ifndef FUTEX_WAIT_REQUEUE_PI_PRIVATE
> #define FUTEX_WAIT_REQUEUE_PI_PRIVATE (FUTEX_WAIT_REQUEUE_PI | \
> FUTEX_PRIVATE_FLAG)
> @@ -86,6 +89,9 @@ int _verbose = VCRITICAL;
> #define FUTEX_CMP_REQUEUE_PI_PRIVATE (FUTEX_CMP_REQUEUE_PI | \
> FUTEX_PRIVATE_FLAG)
> #endif
> +#ifndef FUTEX_SET_WAIT_PRIVATE
> +#define FUTEX_SET_WAIT_PRIVATE (FUTEX_SET_WAIT | FUTEX_PRIVATE_FLAG)
> +#endif
>
> /**
> * futex() - SYS_futex syscall wrapper
> @@ -106,7 +112,7 @@ int _verbose = VCRITICAL;
> * like-named arguments in the following wrappers except where noted below.
> */
> #define futex(uaddr, op, val, timeout, uaddr2, val3, opflags) \
> - syscall(SYS_futex, uaddr, op | opflags, val, timeout, uaddr2, val3);
> + syscall(SYS_futex, uaddr, op | opflags, val, timeout, uaddr2, val3)
>
> /**
> * futex_wait() - block on uaddr with optional timeout
> @@ -119,8 +125,8 @@ int _verbose = VCRITICAL;
> * futex_wake() - wake one or more tasks blocked on uaddr
> * @nr_wake: wake up to this many tasks
> */
> -#define futex_wake(uaddr, val, nr_wake, opflags) \
> - futex(uaddr, FUTEX_WAKE, val, NULL, NULL, nr_wake, opflags)
> +#define futex_wake(uaddr, nr_wake, opflags) \
> + futex(uaddr, FUTEX_WAKE, nr_wake, NULL, NULL, 0, opflags)
>
> /**
> * futex_wait_bitset() - block on uaddr with bitset
> @@ -133,8 +139,8 @@ int _verbose = VCRITICAL;
> * futex_wake_bitset() - wake one or more tasks blocked on uaddr with bitset
> * @bitset: bitset to compare with that used in futex_wait_bitset
> */
> -#define futex_wake_bitset(uaddr, val, nr_wake, bitset, opflags) \
> - futex(uaddr, FUTEX_WAKE_BITSET, val, NULL, NULL, bitset, opflags)
> +#define futex_wake_bitset(uaddr, nr_wake, bitset, opflags) \
> + futex(uaddr, FUTEX_WAKE_BITSET, nr_wake, NULL, NULL, bitset, opflags)
>
> /**
> * futex_lock_pi() - block on uaddr as a PI mutex
> @@ -198,6 +204,14 @@ int _verbose = VCRITICAL;
> opflags)
>
> /**
> + * futex_set_wait() - block on uaddr with bitset
> + * @setval: value to set futex to if blocking
> + * @bitset: bitset to be used with futex_wake_bitset
> + */
> +#define futex_set_wait(uaddr, val, setval, timeout, bitset, opflags) \
> + futex(uaddr, FUTEX_SET_WAIT, val, timeout, setval, bitset, opflags)
> +
> +/**
> * futex_cmpxchg() - Atomic compare and exchange
> * @uaddr: The address of the futex to be modified
> * @oldval: The expected value of the futex
> diff --git a/performance/Makefile b/performance/Makefile
> index 9589e49..c4999a8 100644
> --- a/performance/Makefile
> +++ b/performance/Makefile
> @@ -3,7 +3,7 @@ CFLAGS := $(CFLAGS) -g -O2 -Wall -D_GNU_SOURCE $(INCLUDES)
> LDFLAGS := $(LDFLAGS) -lpthread -lrt
>
> HEADERS := ../include/futextest.h
> -TARGETS :=
> +TARGETS := futex_wait_test futex_setwait_test
>
> .PHONY: all clean
> all: $(TARGETS)
> diff --git a/performance/futex_setwait_test.c b/performance/futex_setwait_test.c
> new file mode 100644
> index 0000000..0d09365
> --- /dev/null
> +++ b/performance/futex_setwait_test.c
> @@ -0,0 +1,71 @@
> +// Copyright 2009 Google Inc.
> +// Author: walken@google.com (Michel Lespinasse)
> +
> +#include "futextest.h"
> +#include "harness.h"
> +
> +#include <stdio.h>
> +#include <errno.h>
> +
> +
> +static inline void futex_setwait_lock(futex_t *futex)
> +{
> + int status = *futex;
> + if (status == 0)
> + status = futex_cmpxchg(futex, 0, 1);
> + if (status != 0) {
> + int desired_status = 1;
> + do {
> + if (futex_set_wait(futex, 1, 2, NULL, ~0,
> + FUTEX_PRIVATE_FLAG) == 0) {
> + /* We absorbed a wakeup; so make sure to
> + unblock next thread */
> + desired_status = 2;
> + }
> + status = *futex;
> + if (status == 0)
> + status = futex_cmpxchg(futex, 0,
> + desired_status);
> + } while (status != 0);
> + }
> +}
> +
> +static inline void futex_cmpxchg_unlock(futex_t *futex)
> +{
> + int status = *futex;
> + if (status == 1)
> + status = futex_cmpxchg(futex, 1, 0);
> + if (status == 2) {
> + futex_cmpxchg(futex, 2, 0);
> + futex_wake(futex, 1, FUTEX_PRIVATE_FLAG);
> + }
> +}
> +
> +static void * futex_setwait_test(void * dummy)
> +{
> + struct locktest_shared * shared = dummy;
> + int i = shared->loops;
> + barrier_sync(&shared->barrier_before);
> + while (i--) {
> + futex_setwait_lock(&shared->futex);
> + futex_cmpxchg_unlock(&shared->futex);
> + }
> + barrier_sync(&shared->barrier_after);
> + return NULL;
> +}
> +
> +static int futex_setwait_supported(void)
> +{
> + int futex = 0;
> + futex_set_wait(futex, 1, 2, NULL, ~0, FUTEX_PRIVATE_FLAG);
> + return errno == EWOULDBLOCK;
> +}
> +
> +int main (void)
> +{
> + if (futex_setwait_supported()) {
> + printf("\nFUTEX_SET_WAIT test\n");
> + locktest(futex_setwait_test, 100000000);
> + }
> + return 0;
> +}
> diff --git a/performance/futex_wait_test.c b/performance/futex_wait_test.c
> new file mode 100644
> index 0000000..88ce2f2
> --- /dev/null
> +++ b/performance/futex_wait_test.c
> @@ -0,0 +1,56 @@
> +// Copyright 2009 Google Inc.
> +// Author: walken@google.com (Michel Lespinasse)
> +
> +#include "futextest.h"
> +#include "harness.h"
> +
> +#include <stdio.h>
> +
> +
> +static inline void futex_wait_lock(futex_t *futex)
> +{
> + int status = *futex;
> + if (status == 0)
> + status = futex_cmpxchg(futex, 0, 1);
> + while (status != 0) {
> + if (status == 1)
> + status = futex_cmpxchg(futex, 1, 2);
> + if (status != 0) {
> + futex_wait(futex, 2, NULL, FUTEX_PRIVATE_FLAG);
> + status = *futex;
> + }
> + if (status == 0)
> + status = futex_cmpxchg(futex, 0, 2);
> + }
> +}
> +
> +static inline void futex_cmpxchg_unlock(futex_t *futex)
> +{
> + int status = *futex;
> + if (status == 1)
> + status = futex_cmpxchg(futex, 1, 0);
> + if (status == 2) {
> + futex_cmpxchg(futex, 2, 0);
> + futex_wake(futex, 1, FUTEX_PRIVATE_FLAG);
> + }
> +}
> +
> +static void * futex_wait_test(void * dummy)
> +{
> + struct locktest_shared * shared = dummy;
> + int i = shared->loops;
> + barrier_sync(&shared->barrier_before);
> + while (i--) {
> + futex_wait_lock(&shared->futex);
> + futex_cmpxchg_unlock(&shared->futex);
> + }
> + barrier_sync(&shared->barrier_after);
> + return NULL;
> +}
> +
> +int main (void)
> +{
> + printf("FUTEX_WAIT test\n");
> + locktest(futex_wait_test, 100000000);
> + return 0;
> +}
> diff --git a/performance/harness.h b/performance/harness.h
> new file mode 100644
> index 0000000..9d74d17
> --- /dev/null
> +++ b/performance/harness.h
> @@ -0,0 +1,103 @@
> +// Copyright 2009 Google Inc.
> +// Author: walken@google.com (Michel Lespinasse)
> +
> +#include <limits.h>
> +#include <sys/times.h>
> +#include <stdio.h>
> +#include <pthread.h>
> +
> +
> +struct thread_barrier {
> + futex_t threads;
> + futex_t unblock;
> +};
> +
> +struct locktest_shared {
> + struct thread_barrier barrier_before;
> + struct thread_barrier barrier_after;
> + int loops;
> + futex_t futex;
> +};
> +
> +static inline void decrement(futex_t *ptr)
> +{
> + __sync_fetch_and_add(ptr, -1);
> +}
> +
> +/* Called by main thread to initialize barrier */
> +static void barrier_init(struct thread_barrier *barrier, int threads)
> +{
> + barrier->threads = threads;
> + barrier->unblock = 0;
> +}
> +
> +/* Called by worker threads to synchronize with main thread */
> +static void barrier_sync(struct thread_barrier *barrier)
> +{
> + decrement(&barrier->threads);
> + if (barrier->threads == 0)
> + futex_wake(&barrier->threads, 1, FUTEX_PRIVATE_FLAG);
> + while (barrier->unblock == 0)
> + futex_wait(&barrier->unblock, 0, NULL, FUTEX_PRIVATE_FLAG);
> +}
> +
> +/* Called by main thread to wait for all workers to reach sync point */
> +static void barrier_wait(struct thread_barrier *barrier)
> +{
> + int threads;
> + while ((threads = barrier->threads) > 0)
> + futex_wait(&barrier->threads, threads, NULL,
> + FUTEX_PRIVATE_FLAG);
> +}
> +
> +/* Called by main thread to unblock worker threads from their sync point */
> +static void barrier_unblock(struct thread_barrier *barrier)
> +{
> + barrier->unblock = 1;
> + futex_wake(&barrier->unblock, INT_MAX, FUTEX_PRIVATE_FLAG);
> +}
> +
> +
> +static void locktest(void * thread_function(void *), int iterations)
> +{
> + int threads[] = { 1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 24, 32,
> + 64, 128, 256, 512, 1024, 0 };
> + int t;
> + for (t = 0; threads[t]; t++) {
> + int num_threads = threads[t];
> + struct locktest_shared shared;
> + pthread_t thread[num_threads];
> + int i;
> + clock_t before, after;
> + struct tms tms_before, tms_after;
> + int wall, user, system;
> + double tick;
> +
> + barrier_init(&shared.barrier_before, num_threads);
> + barrier_init(&shared.barrier_after, num_threads);
> + shared.loops = iterations / num_threads;
> + shared.futex = 0;
> +
> + for (i = 0; i < num_threads; i++)
> + pthread_create(thread + i, NULL, thread_function,
> + &shared);
> + barrier_wait(&shared.barrier_before);
> + before = times(&tms_before);
> + barrier_unblock(&shared.barrier_before);
> + barrier_wait(&shared.barrier_after);
> + after = times(&tms_after);
> + wall = after - before;
> + user = tms_after.tms_utime - tms_before.tms_utime;
> + system = tms_after.tms_stime - tms_before.tms_stime;
> + tick = 1.0 / sysconf(_SC_CLK_TCK);
> + printf("%d threads: %.0f Kiter/s "
> + "(%.2fs user %.2fs system %.2fs wall %.2f cores)\n",
> + num_threads,
> + (num_threads * shared.loops) / (wall * tick * 1000),
> + user * tick, system * tick, wall * tick,
> + wall ? (user + system) * 1. / wall : 1.);
> + barrier_unblock(&shared.barrier_after);
> + for (i = 0; i < num_threads; i++)
> + pthread_join(thread[i], NULL);
> + }
> +}
>
>

--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team