[Qemu-devel] [PATCH v7 0/3] High downtime with 95+ throttle pct

[Qemu-devel] [PATCH v7 0/3] High downtime with 95+ throttle pct

[Yury Kotov]

Hi,

V7:
* Fix memory leak in the auto converge test

V6:
* Fix "Add qemu_cond_timedwait" patch:
  - Changed return type for qemu_cond_timedwait (void -> bool)
  - Added details in commit message

V5:
* Updated sleep loop in throttle_thread at the suggestion of Paolo Bonzini
* Fixed hanging of test

V4:
* The test was simplified to prevent false fails.

V3:
* Rebase fixes (migrate_set_parameter -> migrate_set_parameter_int)

V2:
* Added a test
* Fixed qemu_cond_timedwait for qsp

I wrote a test for migration auto converge and found out a strange thing:
1. Enable auto converge
2. Set max-bandwidth 1Gb/s
3. Set downtime-limit 1ms
4. Run standard test (just writes a byte per page)
5. Wait for converge
6. It's converged with 99% throttle percentage
7. The result downtime was about 300-600ms   <<<<

It's much higher than expected 1ms. I figured out that cpu_throttle_thread()
function sleeps for 100ms+ for high throttle percentage (>=95%) in VCPU thread.
And it sleeps even after a cpu kick.

Fixed it by using timedwait for ms part of sleep.
E.g timedwait(halt_cond, 1ms) + usleep(500).

Regards,
Yury

Yury Kotov (3):
  qemu-thread: Add qemu_cond_timedwait
  cpus: Fix throttling during vm_stop
  tests/migration: Add a test for auto converge

 cpus.c                   |  25 +++++---
 include/qemu/thread.h    |  19 ++++++
 tests/migration-test.c   | 130 +++++++++++++++++++++++++++++++++++----
 util/qemu-thread-posix.c |  41 ++++++++----
 util/qemu-thread-win32.c |  17 +++++
 util/qsp.c               |  20 ++++++
 6 files changed, 221 insertions(+), 31 deletions(-)

-- 
2.23.0

[Qemu-devel] [PATCH v7 1/3] qemu-thread: Add qemu_cond_timedwait

[Yury Kotov]

The new function is needed to implement conditional sleep for CPU
throttling. It's possible to reuse qemu_sem_timedwait, but it's more
difficult than just add qemu_cond_timedwait.

Also moved compute_abs_deadline function up the code to reuse it in
qemu_cond_timedwait_impl win32.

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
---
 include/qemu/thread.h    | 19 +++++++++++++++++++
 util/qemu-thread-posix.c | 41 ++++++++++++++++++++++++++++------------
 util/qemu-thread-win32.c | 17 +++++++++++++++++
 util/qsp.c               | 20 ++++++++++++++++++++
 4 files changed, 85 insertions(+), 12 deletions(-)

diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index 55d83a907c..047db0307e 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -34,6 +34,8 @@ typedef void (*QemuRecMutexLockFunc)(QemuRecMutex *m, const char *f, int l);
 typedef int (*QemuRecMutexTrylockFunc)(QemuRecMutex *m, const char *f, int l);
 typedef void (*QemuCondWaitFunc)(QemuCond *c, QemuMutex *m, const char *f,
                                  int l);
+typedef bool (*QemuCondTimedWaitFunc)(QemuCond *c, QemuMutex *m, int ms,
+                                      const char *f, int l);
 
 extern QemuMutexLockFunc qemu_bql_mutex_lock_func;
 extern QemuMutexLockFunc qemu_mutex_lock_func;
@@ -41,6 +43,7 @@ extern QemuMutexTrylockFunc qemu_mutex_trylock_func;
 extern QemuRecMutexLockFunc qemu_rec_mutex_lock_func;
 extern QemuRecMutexTrylockFunc qemu_rec_mutex_trylock_func;
 extern QemuCondWaitFunc qemu_cond_wait_func;
+extern QemuCondTimedWaitFunc qemu_cond_timedwait_func;
 
 /* convenience macros to bypass the profiler */
 #define qemu_mutex_lock__raw(m)                         \
@@ -63,6 +66,8 @@ extern QemuCondWaitFunc qemu_cond_wait_func;
             qemu_rec_mutex_trylock_impl(m, __FILE__, __LINE__);
 #define qemu_cond_wait(c, m)                                            \
             qemu_cond_wait_impl(c, m, __FILE__, __LINE__);
+#define qemu_cond_timedwait(c, m, ms)                                   \
+            qemu_cond_wait_impl(c, m, ms, __FILE__, __LINE__);
 #else
 #define qemu_mutex_lock(m) ({                                           \
             QemuMutexLockFunc _f = atomic_read(&qemu_mutex_lock_func);  \
@@ -89,6 +94,11 @@ extern QemuCondWaitFunc qemu_cond_wait_func;
             QemuCondWaitFunc _f = atomic_read(&qemu_cond_wait_func);    \
             _f(c, m, __FILE__, __LINE__);                               \
         })
+
+#define qemu_cond_timedwait(c, m, ms) ({                                       \
+            QemuCondTimedWaitFunc _f = atomic_read(&qemu_cond_timedwait_func); \
+            _f(c, m, ms, __FILE__, __LINE__);                                  \
+        })
 #endif
 
 #define qemu_mutex_unlock(mutex) \
@@ -134,12 +144,21 @@ void qemu_cond_signal(QemuCond *cond);
 void qemu_cond_broadcast(QemuCond *cond);
 void qemu_cond_wait_impl(QemuCond *cond, QemuMutex *mutex,
                          const char *file, const int line);
+bool qemu_cond_timedwait_impl(QemuCond *cond, QemuMutex *mutex, int ms,
+                              const char *file, const int line);
 
 static inline void (qemu_cond_wait)(QemuCond *cond, QemuMutex *mutex)
 {
     qemu_cond_wait(cond, mutex);
 }
 
+/* Returns true if timeout has not expired, and false otherwise */
+static inline bool (qemu_cond_timedwait)(QemuCond *cond, QemuMutex *mutex,
+                                         int ms)
+{
+    return qemu_cond_timedwait(cond, mutex, ms);
+}
+
 void qemu_sem_init(QemuSemaphore *sem, int init);
 void qemu_sem_post(QemuSemaphore *sem);
 void qemu_sem_wait(QemuSemaphore *sem);
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index 1bf5e65dea..838980aaa5 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -36,6 +36,18 @@ static void error_exit(int err, const char *msg)
     abort();
 }
 
+static void compute_abs_deadline(struct timespec *ts, int ms)
+{
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    ts->tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
+    ts->tv_sec = tv.tv_sec + ms / 1000;
+    if (ts->tv_nsec >= 1000000000) {
+        ts->tv_sec++;
+        ts->tv_nsec -= 1000000000;
+    }
+}
+
 void qemu_mutex_init(QemuMutex *mutex)
 {
     int err;
@@ -164,6 +176,23 @@ void qemu_cond_wait_impl(QemuCond *cond, QemuMutex *mutex, const char *file, con
         error_exit(err, __func__);
 }
 
+bool qemu_cond_timedwait_impl(QemuCond *cond, QemuMutex *mutex, int ms,
+                              const char *file, const int line)
+{
+    int err;
+    struct timespec ts;
+
+    assert(cond->initialized);
+    trace_qemu_mutex_unlock(mutex, file, line);
+    compute_abs_deadline(&ts, ms);
+    err = pthread_cond_timedwait(&cond->cond, &mutex->lock, &ts);
+    trace_qemu_mutex_locked(mutex, file, line);
+    if (err && err != ETIMEDOUT) {
+        error_exit(err, __func__);
+    }
+    return err != ETIMEDOUT;
+}
+
 void qemu_sem_init(QemuSemaphore *sem, int init)
 {
     int rc;
@@ -238,18 +267,6 @@ void qemu_sem_post(QemuSemaphore *sem)
 #endif
 }
 
-static void compute_abs_deadline(struct timespec *ts, int ms)
-{
-    struct timeval tv;
-    gettimeofday(&tv, NULL);
-    ts->tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
-    ts->tv_sec = tv.tv_sec + ms / 1000;
-    if (ts->tv_nsec >= 1000000000) {
-        ts->tv_sec++;
-        ts->tv_nsec -= 1000000000;
-    }
-}
-
 int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
 {
     int rc;
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index 572f88535d..56a83333da 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -145,6 +145,23 @@ void qemu_cond_wait_impl(QemuCond *cond, QemuMutex *mutex, const char *file, con
     qemu_mutex_post_lock(mutex, file, line);
 }
 
+bool qemu_cond_timedwait_impl(QemuCond *cond, QemuMutex *mutex, int ms,
+                              const char *file, const int line)
+{
+    int rc = 0;
+
+    assert(cond->initialized);
+    trace_qemu_mutex_unlock(mutex, file, line);
+    if (!SleepConditionVariableSRW(&cond->var, &mutex->lock, ms, 0)) {
+        rc = GetLastError();
+    }
+    trace_qemu_mutex_locked(mutex, file, line);
+    if (rc && rc != ERROR_TIMEOUT) {
+        error_exit(rc, __func__);
+    }
+    return rc != ERROR_TIMEOUT;
+}
+
 void qemu_sem_init(QemuSemaphore *sem, int init)
 {
     /* Manual reset.  */
diff --git a/util/qsp.c b/util/qsp.c
index 5264c97342..62265417fd 100644
--- a/util/qsp.c
+++ b/util/qsp.c
@@ -131,6 +131,7 @@ QemuRecMutexLockFunc qemu_rec_mutex_lock_func = qemu_rec_mutex_lock_impl;
 QemuRecMutexTrylockFunc qemu_rec_mutex_trylock_func =
     qemu_rec_mutex_trylock_impl;
 QemuCondWaitFunc qemu_cond_wait_func = qemu_cond_wait_impl;
+QemuCondTimedWaitFunc qemu_cond_timedwait_func = qemu_cond_timedwait_impl;
 
 /*
  * It pays off to _not_ hash callsite->file; hashing a string is slow, and
@@ -412,6 +413,23 @@ qsp_cond_wait(QemuCond *cond, QemuMutex *mutex, const char *file, int line)
     qsp_entry_record(e, t1 - t0);
 }
 
+static bool
+qsp_cond_timedwait(QemuCond *cond, QemuMutex *mutex, int ms,
+                   const char *file, int line)
+{
+    QSPEntry *e;
+    int64_t t0, t1;
+    bool ret;
+
+    t0 = get_clock();
+    ret = qemu_cond_timedwait_impl(cond, mutex, ms, file, line);
+    t1 = get_clock();
+
+    e = qsp_entry_get(cond, file, line, QSP_CONDVAR);
+    qsp_entry_record(e, t1 - t0);
+    return ret;
+}
+
 bool qsp_is_enabled(void)
 {
     return atomic_read(&qemu_mutex_lock_func) == qsp_mutex_lock;
@@ -425,6 +443,7 @@ void qsp_enable(void)
     atomic_set(&qemu_rec_mutex_lock_func, qsp_rec_mutex_lock);
     atomic_set(&qemu_rec_mutex_trylock_func, qsp_rec_mutex_trylock);
     atomic_set(&qemu_cond_wait_func, qsp_cond_wait);
+    atomic_set(&qemu_cond_timedwait_func, qsp_cond_timedwait);
 }
 
 void qsp_disable(void)
@@ -435,6 +454,7 @@ void qsp_disable(void)
     atomic_set(&qemu_rec_mutex_lock_func, qemu_rec_mutex_lock_impl);
     atomic_set(&qemu_rec_mutex_trylock_func, qemu_rec_mutex_trylock_impl);
     atomic_set(&qemu_cond_wait_func, qemu_cond_wait_impl);
+    atomic_set(&qemu_cond_timedwait_func, qemu_cond_timedwait_impl);
 }
 
 static gint qsp_tree_cmp(gconstpointer ap, gconstpointer bp, gpointer up)
-- 
2.23.0

[Qemu-devel] [PATCH v7 2/3] cpus: Fix throttling during vm_stop

[Yury Kotov]

Throttling thread sleeps in VCPU thread. For high throttle percentage
this sleep is more than 10ms. E.g. for 60% - 15ms, for 99% - 990ms.
vm_stop() kicks all VCPUs and waits for them. It's called at the end of
migration and because of the long sleep the migration downtime might be
more than 100ms even for downtime-limit 1ms.
Use qemu_cond_timedwait for high percentage to wake up during vm_stop.

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 cpus.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/cpus.c b/cpus.c
index 85cd451a86..d2c61ff155 100644
--- a/cpus.c
+++ b/cpus.c
@@ -77,6 +77,8 @@
 
 #endif /* CONFIG_LINUX */
 
+static QemuMutex qemu_global_mutex;
+
 int64_t max_delay;
 int64_t max_advance;
 
@@ -782,7 +784,7 @@ static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque)
 {
     double pct;
     double throttle_ratio;
-    long sleeptime_ns;
+    int64_t sleeptime_ns, endtime_ns;
 
     if (!cpu_throttle_get_percentage()) {
         return;
@@ -790,11 +792,20 @@ static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque)
 
     pct = (double)cpu_throttle_get_percentage()/100;
     throttle_ratio = pct / (1 - pct);
-    sleeptime_ns = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS);
-
-    qemu_mutex_unlock_iothread();
-    g_usleep(sleeptime_ns / 1000); /* Convert ns to us for usleep call */
-    qemu_mutex_lock_iothread();
+    /* Add 1ns to fix double's rounding error (like 0.9999999...) */
+    sleeptime_ns = (int64_t)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS + 1);
+    endtime_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + sleeptime_ns;
+    while (sleeptime_ns > 0 && !cpu->stop) {
+        if (sleeptime_ns > SCALE_MS) {
+            qemu_cond_timedwait(cpu->halt_cond, &qemu_global_mutex,
+                                sleeptime_ns / SCALE_MS);
+        } else {
+            qemu_mutex_unlock_iothread();
+            g_usleep(sleeptime_ns / SCALE_US);
+            qemu_mutex_lock_iothread();
+        }
+        sleeptime_ns = endtime_ns - qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
+    }
     atomic_set(&cpu->throttle_thread_scheduled, 0);
 }
 
@@ -1172,8 +1183,6 @@ static void qemu_init_sigbus(void)
 }
 #endif /* !CONFIG_LINUX */
 
-static QemuMutex qemu_global_mutex;
-
 static QemuThread io_thread;
 
 /* cpu creation */
-- 
2.23.0

[Qemu-devel] [PATCH v7 3/3] tests/migration: Add a test for auto converge

[Yury Kotov]

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 tests/migration-test.c | 130 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 119 insertions(+), 11 deletions(-)

diff --git a/tests/migration-test.c b/tests/migration-test.c
index a9f81cc185..966d458d72 100644
--- a/tests/migration-test.c
+++ b/tests/migration-test.c
@@ -240,6 +240,17 @@ static int64_t read_ram_property_int(QTestState *who, const char *property)
     return result;
 }
 
+static int64_t read_migrate_property_int(QTestState *who, const char *property)
+{
+    QDict *rsp_return;
+    int64_t result;
+
+    rsp_return = migrate_query(who);
+    result = qdict_get_try_int(rsp_return, property, 0);
+    qobject_unref(rsp_return);
+    return result;
+}
+
 static uint64_t get_migration_pass(QTestState *who)
 {
     return read_ram_property_int(who, "dirty-sync-count");
@@ -254,20 +265,22 @@ static void read_blocktime(QTestState *who)
     qobject_unref(rsp_return);
 }
 
+static bool check_migration_status(QTestState *who, const char *status)
+{
+    bool completed;
+    char *current_status;
+
+    current_status = migrate_query_status(who);
+    completed = strcmp(current_status, status) == 0;
+    g_assert_cmpstr(current_status, !=, "failed");
+    g_free(current_status);
+    return completed;
+}
+
 static void wait_for_migration_status(QTestState *who,
                                       const char *goal)
 {
-    while (true) {
-        bool completed;
-        char *status;
-
-        status = migrate_query_status(who);
-        completed = strcmp(status, goal) == 0;
-        g_assert_cmpstr(status, !=,  "failed");
-        g_free(status);
-        if (completed) {
-            return;
-        }
+    while (!check_migration_status(who, goal)) {
         usleep(1000);
     }
 }
@@ -445,6 +458,17 @@ static void migrate_pause(QTestState *who)
     qobject_unref(rsp);
 }
 
+static void migrate_continue(QTestState *who, const char *state)
+{
+    QDict *rsp;
+
+    rsp = wait_command(who,
+                       "{ 'execute': 'migrate-continue',"
+                       "  'arguments': { 'state': %s } }",
+                       state);
+    qobject_unref(rsp);
+}
+
 static void migrate_recover(QTestState *who, const char *uri)
 {
     QDict *rsp;
@@ -1125,6 +1149,89 @@ static void test_migrate_fd_proto(void)
     test_migrate_end(from, to, true);
 }
 
+static void test_migrate_auto_converge(void)
+{
+    char *uri = g_strdup_printf("unix:%s/migsocket", tmpfs);
+    QTestState *from, *to;
+    int64_t remaining, percentage;
+
+    /*
+     * We want the test to be stable and as fast as possible.
+     * E.g., with 1Gb/s bandwith migration may pass without throttling,
+     * so we need to decrease a bandwidth.
+     */
+    const int64_t init_pct = 5, inc_pct = 50, max_pct = 95;
+    const int64_t max_bandwidth = 400000000; /* ~400Mb/s */
+    const int64_t downtime_limit = 250; /* 250ms */
+    /*
+     * We migrate through unix-socket (> 500Mb/s).
+     * Thus, expected migration speed ~= bandwidth limit (< 500Mb/s).
+     * So, we can predict expected_threshold
+     */
+    const int64_t expected_threshold = max_bandwidth * downtime_limit / 1000;
+
+    if (test_migrate_start(&from, &to, uri, false, false)) {
+        return;
+    }
+
+    migrate_set_capability(from, "auto-converge", true);
+    migrate_set_parameter_int(from, "cpu-throttle-initial", init_pct);
+    migrate_set_parameter_int(from, "cpu-throttle-increment", inc_pct);
+    migrate_set_parameter_int(from, "max-cpu-throttle", max_pct);
+
+    /*
+     * Set the initial parameters so that the migration could not converge
+     * without throttling.
+     */
+    migrate_set_parameter_int(from, "downtime-limit", 1);
+    migrate_set_parameter_int(from, "max-bandwidth", 100000000); /* ~100Mb/s */
+
+    /* To check remaining size after precopy */
+    migrate_set_capability(from, "pause-before-switchover", true);
+
+    /* Wait for the first serial output from the source */
+    wait_for_serial("src_serial");
+
+    migrate(from, uri, "{}");
+
+    /* Wait for throttling begins */
+    percentage = 0;
+    while (percentage == 0) {
+        percentage = read_migrate_property_int(from, "cpu-throttle-percentage");
+        usleep(100);
+        g_assert_false(got_stop);
+    }
+    /* The first percentage of throttling should be equal to init_pct */
+    g_assert_cmpint(percentage, ==, init_pct);
+    /* Now, when we tested that throttling works, let it converge */
+    migrate_set_parameter_int(from, "downtime-limit", downtime_limit);
+    migrate_set_parameter_int(from, "max-bandwidth", max_bandwidth);
+
+    /*
+     * Wait for pre-switchover status to check last throttle percentage
+     * and remaining. These values will be zeroed later
+     */
+    wait_for_migration_status(from, "pre-switchover");
+
+    /* The final percentage of throttling shouldn't be greater than max_pct */
+    percentage = read_migrate_property_int(from, "cpu-throttle-percentage");
+    g_assert_cmpint(percentage, <=, max_pct);
+
+    remaining = read_ram_property_int(from, "remaining");
+    g_assert_cmpint(remaining, <, expected_threshold);
+
+    migrate_continue(from, "pre-switchover");
+
+    qtest_qmp_eventwait(to, "RESUME");
+
+    wait_for_serial("dest_serial");
+    wait_for_migration_complete(from);
+
+    g_free(uri);
+
+    test_migrate_end(from, to, true);
+}
+
 int main(int argc, char **argv)
 {
     char template[] = "/tmp/migration-test-XXXXXX";
@@ -1180,6 +1287,7 @@ int main(int argc, char **argv)
     /* qtest_add_func("/migration/ignore_shared", test_ignore_shared); */
     qtest_add_func("/migration/xbzrle/unix", test_xbzrle_unix);
     qtest_add_func("/migration/fd_proto", test_migrate_fd_proto);
+    qtest_add_func("/migration/auto_converge", test_migrate_auto_converge);
 
     ret = g_test_run();
 
-- 
2.23.0