qemu/tests/rcutorture.c
Alex Bennée a74c82c8dc tests/rcutorture: mild documenting refactor of update thread
This is mainly to help with reasoning what the test is trying to do.
We can move rcu_stress_idx to a local variable as there is only ever
one updater thread. I've also added an assert to catch the case where
we end up updating the current structure to itself which is the only
way I can see the mberror cases we are seeing on Travis.

We shall see if the rcutorture test failures go away now.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Message-Id: <20200225124710.14152-5-alex.bennee@linaro.org>
2020-02-25 17:42:59 +00:00

484 lines
13 KiB
C

/*
* rcutorture.c: simple user-level performance/stress test of RCU.
*
* Usage:
* ./rcu <nreaders> rperf [ <seconds> ]
* Run a read-side performance test with the specified
* number of readers for <seconds> seconds.
* ./rcu <nupdaters> uperf [ <seconds> ]
* Run an update-side performance test with the specified
* number of updaters and specified duration.
* ./rcu <nreaders> perf [ <seconds> ]
* Run a combined read/update performance test with the specified
* number of readers and one updater and specified duration.
*
* The above tests produce output as follows:
*
* n_reads: 46008000 n_updates: 146026 nreaders: 2 nupdaters: 1 duration: 1
* ns/read: 43.4707 ns/update: 6848.1
*
* The first line lists the total number of RCU reads and updates executed
* during the test, the number of reader threads, the number of updater
* threads, and the duration of the test in seconds. The second line
* lists the average duration of each type of operation in nanoseconds,
* or "nan" if the corresponding type of operation was not performed.
*
* ./rcu <nreaders> stress [ <seconds> ]
* Run a stress test with the specified number of readers and
* one updater.
*
* This test produces output as follows:
*
* n_reads: 114633217 n_updates: 3903415 n_mberror: 0
* rcu_stress_count: 114618391 14826 0 0 0 0 0 0 0 0 0
*
* The first line lists the number of RCU read and update operations
* executed, followed by the number of memory-ordering violations
* (which will be zero in a correct RCU implementation). The second
* line lists the number of readers observing progressively more stale
* data. A correct RCU implementation will have all but the first two
* numbers non-zero.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (c) 2008 Paul E. McKenney, IBM Corporation.
*/
/*
* Test variables.
*/
#include "qemu/osdep.h"
#include "qemu/atomic.h"
#include "qemu/rcu.h"
#include "qemu/thread.h"
int nthreadsrunning;
#define GOFLAG_INIT 0
#define GOFLAG_RUN 1
#define GOFLAG_STOP 2
static volatile int goflag = GOFLAG_INIT;
#define RCU_READ_RUN 1000
#define NR_THREADS 100
static QemuThread threads[NR_THREADS];
static struct rcu_reader_data *data[NR_THREADS];
static int n_threads;
/*
* Statistical counts
*
* These are the sum of local counters at the end of a run.
* Updates are protected by a mutex.
*/
static QemuMutex counts_mutex;
long long n_reads = 0LL;
long n_updates = 0L;
static void create_thread(void *(*func)(void *))
{
if (n_threads >= NR_THREADS) {
fprintf(stderr, "Thread limit of %d exceeded!\n", NR_THREADS);
exit(-1);
}
qemu_thread_create(&threads[n_threads], "test", func, &data[n_threads],
QEMU_THREAD_JOINABLE);
n_threads++;
}
static void wait_all_threads(void)
{
int i;
for (i = 0; i < n_threads; i++) {
qemu_thread_join(&threads[i]);
}
n_threads = 0;
}
/*
* Performance test.
*/
static void *rcu_read_perf_test(void *arg)
{
int i;
long long n_reads_local = 0;
rcu_register_thread();
*(struct rcu_reader_data **)arg = &rcu_reader;
atomic_inc(&nthreadsrunning);
while (goflag == GOFLAG_INIT) {
g_usleep(1000);
}
while (goflag == GOFLAG_RUN) {
for (i = 0; i < RCU_READ_RUN; i++) {
rcu_read_lock();
rcu_read_unlock();
}
n_reads_local += RCU_READ_RUN;
}
qemu_mutex_lock(&counts_mutex);
n_reads += n_reads_local;
qemu_mutex_unlock(&counts_mutex);
rcu_unregister_thread();
return NULL;
}
static void *rcu_update_perf_test(void *arg)
{
long long n_updates_local = 0;
rcu_register_thread();
*(struct rcu_reader_data **)arg = &rcu_reader;
atomic_inc(&nthreadsrunning);
while (goflag == GOFLAG_INIT) {
g_usleep(1000);
}
while (goflag == GOFLAG_RUN) {
synchronize_rcu();
n_updates_local++;
}
qemu_mutex_lock(&counts_mutex);
n_updates += n_updates_local;
qemu_mutex_unlock(&counts_mutex);
rcu_unregister_thread();
return NULL;
}
static void perftestinit(void)
{
nthreadsrunning = 0;
}
static void perftestrun(int nthreads, int duration, int nreaders, int nupdaters)
{
while (atomic_read(&nthreadsrunning) < nthreads) {
g_usleep(1000);
}
goflag = GOFLAG_RUN;
g_usleep(duration * G_USEC_PER_SEC);
goflag = GOFLAG_STOP;
wait_all_threads();
printf("n_reads: %lld n_updates: %ld nreaders: %d nupdaters: %d duration: %d\n",
n_reads, n_updates, nreaders, nupdaters, duration);
printf("ns/read: %g ns/update: %g\n",
((duration * 1000*1000*1000.*(double)nreaders) /
(double)n_reads),
((duration * 1000*1000*1000.*(double)nupdaters) /
(double)n_updates));
exit(0);
}
static void perftest(int nreaders, int duration)
{
int i;
perftestinit();
for (i = 0; i < nreaders; i++) {
create_thread(rcu_read_perf_test);
}
create_thread(rcu_update_perf_test);
perftestrun(i + 1, duration, nreaders, 1);
}
static void rperftest(int nreaders, int duration)
{
int i;
perftestinit();
for (i = 0; i < nreaders; i++) {
create_thread(rcu_read_perf_test);
}
perftestrun(i, duration, nreaders, 0);
}
static void uperftest(int nupdaters, int duration)
{
int i;
perftestinit();
for (i = 0; i < nupdaters; i++) {
create_thread(rcu_update_perf_test);
}
perftestrun(i, duration, 0, nupdaters);
}
/*
* Stress test.
*/
#define RCU_STRESS_PIPE_LEN 10
struct rcu_stress {
int age; /* how many update cycles while not rcu_stress_current */
int mbtest;
};
struct rcu_stress rcu_stress_array[RCU_STRESS_PIPE_LEN] = { { 0 } };
struct rcu_stress *rcu_stress_current;
int n_mberror;
/* Updates protected by counts_mutex */
long long rcu_stress_count[RCU_STRESS_PIPE_LEN + 1];
static void *rcu_read_stress_test(void *arg)
{
int i;
struct rcu_stress *p;
int pc;
long long n_reads_local = 0;
long long rcu_stress_local[RCU_STRESS_PIPE_LEN + 1] = { 0 };
volatile int garbage = 0;
rcu_register_thread();
*(struct rcu_reader_data **)arg = &rcu_reader;
while (goflag == GOFLAG_INIT) {
g_usleep(1000);
}
while (goflag == GOFLAG_RUN) {
rcu_read_lock();
p = atomic_rcu_read(&rcu_stress_current);
if (atomic_read(&p->mbtest) == 0) {
n_mberror++;
}
rcu_read_lock();
for (i = 0; i < 100; i++) {
garbage++;
}
rcu_read_unlock();
pc = atomic_read(&p->age);
rcu_read_unlock();
if ((pc > RCU_STRESS_PIPE_LEN) || (pc < 0)) {
pc = RCU_STRESS_PIPE_LEN;
}
rcu_stress_local[pc]++;
n_reads_local++;
}
qemu_mutex_lock(&counts_mutex);
n_reads += n_reads_local;
for (i = 0; i <= RCU_STRESS_PIPE_LEN; i++) {
rcu_stress_count[i] += rcu_stress_local[i];
}
qemu_mutex_unlock(&counts_mutex);
rcu_unregister_thread();
return NULL;
}
/*
* Stress Test Updater
*
* The updater cycles around updating rcu_stress_current to point at
* one of the rcu_stress_array_entries and resets it's age. It
* then increments the age of all the other entries. The age
* will be read under an rcu_read_lock() and distribution of values
* calculated. The final result gives an indication of how many
* previously current rcu_stress entries are in flight until the RCU
* cycle complete.
*/
static void *rcu_update_stress_test(void *arg)
{
int i, rcu_stress_idx = 0;
struct rcu_stress *cp = atomic_read(&rcu_stress_current);
rcu_register_thread();
*(struct rcu_reader_data **)arg = &rcu_reader;
while (goflag == GOFLAG_INIT) {
g_usleep(1000);
}
while (goflag == GOFLAG_RUN) {
struct rcu_stress *p;
rcu_stress_idx++;
if (rcu_stress_idx >= RCU_STRESS_PIPE_LEN) {
rcu_stress_idx = 0;
}
p = &rcu_stress_array[rcu_stress_idx];
/* catching up with ourselves would be a bug */
assert(p != cp);
atomic_set(&p->mbtest, 0);
smp_mb();
atomic_set(&p->age, 0);
atomic_set(&p->mbtest, 1);
atomic_rcu_set(&rcu_stress_current, p);
cp = p;
/*
* New RCU structure is now live, update pipe counts on old
* ones.
*/
for (i = 0; i < RCU_STRESS_PIPE_LEN; i++) {
if (i != rcu_stress_idx) {
atomic_set(&rcu_stress_array[i].age,
rcu_stress_array[i].age + 1);
}
}
synchronize_rcu();
n_updates++;
}
rcu_unregister_thread();
return NULL;
}
static void *rcu_fake_update_stress_test(void *arg)
{
rcu_register_thread();
*(struct rcu_reader_data **)arg = &rcu_reader;
while (goflag == GOFLAG_INIT) {
g_usleep(1000);
}
while (goflag == GOFLAG_RUN) {
synchronize_rcu();
g_usleep(1000);
}
rcu_unregister_thread();
return NULL;
}
static void stresstest(int nreaders, int duration)
{
int i;
rcu_stress_current = &rcu_stress_array[0];
rcu_stress_current->age = 0;
rcu_stress_current->mbtest = 1;
for (i = 0; i < nreaders; i++) {
create_thread(rcu_read_stress_test);
}
create_thread(rcu_update_stress_test);
for (i = 0; i < 5; i++) {
create_thread(rcu_fake_update_stress_test);
}
goflag = GOFLAG_RUN;
g_usleep(duration * G_USEC_PER_SEC);
goflag = GOFLAG_STOP;
wait_all_threads();
printf("n_reads: %lld n_updates: %ld n_mberror: %d\n",
n_reads, n_updates, n_mberror);
printf("rcu_stress_count:");
for (i = 0; i <= RCU_STRESS_PIPE_LEN; i++) {
printf(" %lld", rcu_stress_count[i]);
}
printf("\n");
exit(0);
}
/* GTest interface */
static void gtest_stress(int nreaders, int duration)
{
int i;
rcu_stress_current = &rcu_stress_array[0];
rcu_stress_current->age = 0;
rcu_stress_current->mbtest = 1;
for (i = 0; i < nreaders; i++) {
create_thread(rcu_read_stress_test);
}
create_thread(rcu_update_stress_test);
for (i = 0; i < 5; i++) {
create_thread(rcu_fake_update_stress_test);
}
goflag = GOFLAG_RUN;
g_usleep(duration * G_USEC_PER_SEC);
goflag = GOFLAG_STOP;
wait_all_threads();
g_assert_cmpint(n_mberror, ==, 0);
for (i = 2; i <= RCU_STRESS_PIPE_LEN; i++) {
g_assert_cmpint(rcu_stress_count[i], ==, 0);
}
}
static void gtest_stress_1_1(void)
{
gtest_stress(1, 1);
}
static void gtest_stress_10_1(void)
{
gtest_stress(10, 1);
}
static void gtest_stress_1_5(void)
{
gtest_stress(1, 5);
}
static void gtest_stress_10_5(void)
{
gtest_stress(10, 5);
}
/*
* Mainprogram.
*/
static void usage(int argc, char *argv[])
{
fprintf(stderr, "Usage: %s [nreaders [ [r|u]perf | stress [duration]]\n",
argv[0]);
exit(-1);
}
int main(int argc, char *argv[])
{
int nreaders = 1;
int duration = 1;
qemu_mutex_init(&counts_mutex);
if (argc >= 2 && argv[1][0] == '-') {
g_test_init(&argc, &argv, NULL);
if (g_test_quick()) {
g_test_add_func("/rcu/torture/1reader", gtest_stress_1_1);
g_test_add_func("/rcu/torture/10readers", gtest_stress_10_1);
} else {
g_test_add_func("/rcu/torture/1reader", gtest_stress_1_5);
g_test_add_func("/rcu/torture/10readers", gtest_stress_10_5);
}
return g_test_run();
}
if (argc >= 2) {
nreaders = strtoul(argv[1], NULL, 0);
}
if (argc > 3) {
duration = strtoul(argv[3], NULL, 0);
}
if (argc < 3 || strcmp(argv[2], "stress") == 0) {
stresstest(nreaders, duration);
} else if (strcmp(argv[2], "rperf") == 0) {
rperftest(nreaders, duration);
} else if (strcmp(argv[2], "uperf") == 0) {
uperftest(nreaders, duration);
} else if (strcmp(argv[2], "perf") == 0) {
perftest(nreaders, duration);
}
usage(argc, argv);
return 0;
}