From bb70b66ed7a5600a63437fb6d64dedb44f670e58 Mon Sep 17 00:00:00 2001 From: Lukas Straub Date: Mon, 11 May 2020 13:10:44 +0200 Subject: [PATCH] migration/colo.c: Use event instead of semaphore If multiple packets miscompare in a short timeframe, the semaphore value will be increased multiple times. This causes multiple checkpoints even if one would be sufficient. Fix this by using a event instead of a semaphore for triggering checkpoints. Now, checkpoint requests will be ignored until the checkpoint event is sent to colo-compare (which releases the miscompared packets). Benchmark results (iperf3): Client-to-server tcp: without patch: ~66 Mbit/s with patch: ~61 Mbit/s Server-to-client tcp: without patch: ~702 Kbit/s with patch: ~16 Mbit/s Signed-off-by: Lukas Straub Message-Id: Reviewed-by: zhanghailiang Signed-off-by: Dr. David Alan Gilbert --- migration/colo.c | 9 +++++---- migration/migration.h | 4 ++-- 2 files changed, 7 insertions(+), 6 deletions(-) diff --git a/migration/colo.c b/migration/colo.c index d015d4f84e..fe0d6e93e5 100644 --- a/migration/colo.c +++ b/migration/colo.c @@ -436,6 +436,7 @@ static int colo_do_checkpoint_transaction(MigrationState *s, goto out; } + qemu_event_reset(&s->colo_checkpoint_event); colo_notify_compares_event(NULL, COLO_EVENT_CHECKPOINT, &local_err); if (local_err) { goto out; @@ -589,7 +590,7 @@ static void colo_process_checkpoint(MigrationState *s) goto out; } - qemu_sem_wait(&s->colo_checkpoint_sem); + qemu_event_wait(&s->colo_checkpoint_event); if (s->state != MIGRATION_STATUS_COLO) { goto out; @@ -637,7 +638,7 @@ out: colo_compare_unregister_notifier(&packets_compare_notifier); timer_del(s->colo_delay_timer); timer_free(s->colo_delay_timer); - qemu_sem_destroy(&s->colo_checkpoint_sem); + qemu_event_destroy(&s->colo_checkpoint_event); /* * Must be called after failover BH is completed, @@ -654,7 +655,7 @@ void colo_checkpoint_notify(void *opaque) MigrationState *s = opaque; int64_t next_notify_time; - qemu_sem_post(&s->colo_checkpoint_sem); + qemu_event_set(&s->colo_checkpoint_event); s->colo_checkpoint_time = qemu_clock_get_ms(QEMU_CLOCK_HOST); next_notify_time = s->colo_checkpoint_time + s->parameters.x_checkpoint_delay; @@ -664,7 +665,7 @@ void colo_checkpoint_notify(void *opaque) void migrate_start_colo_process(MigrationState *s) { qemu_mutex_unlock_iothread(); - qemu_sem_init(&s->colo_checkpoint_sem, 0); + qemu_event_init(&s->colo_checkpoint_event, false); s->colo_delay_timer = timer_new_ms(QEMU_CLOCK_HOST, colo_checkpoint_notify, s); diff --git a/migration/migration.h b/migration/migration.h index 507284e563..f617960522 100644 --- a/migration/migration.h +++ b/migration/migration.h @@ -215,8 +215,8 @@ struct MigrationState /* The semaphore is used to notify COLO thread that failover is finished */ QemuSemaphore colo_exit_sem; - /* The semaphore is used to notify COLO thread to do checkpoint */ - QemuSemaphore colo_checkpoint_sem; + /* The event is used to notify COLO thread to do checkpoint */ + QemuEvent colo_checkpoint_event; int64_t colo_checkpoint_time; QEMUTimer *colo_delay_timer;