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Thu, 12 Oct 2023 14:07:04 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id EFEmN4j9J2U5CgAAMHmgww (envelope-from ); Thu, 12 Oct 2023 14:07:04 +0000 From: Fabiano Rosas To: qemu-devel@nongnu.org Cc: Juan Quintela , Peter Xu , Leonardo Bras , Elena Ufimtseva Subject: [RFC PATCH v2 6/6] migration/multifd: Bring back the 'ready' semaphore Date: Thu, 12 Oct 2023 11:06:51 -0300 Message-Id: <20231012140651.13122-7-farosas@suse.de> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20231012140651.13122-1-farosas@suse.de> References: <20231012140651.13122-1-farosas@suse.de> MIME-Version: 1.0 Authentication-Results: smtp-out2.suse.de; none X-Spam-Score: -2.10 X-Spamd-Result: default: False [-2.10 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; R_MISSING_CHARSET(2.50)[]; MIME_GOOD(-0.10)[text/plain]; BROKEN_CONTENT_TYPE(1.50)[]; RCPT_COUNT_FIVE(0.00)[5]; NEURAL_HAM_LONG(-3.00)[-1.000]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-3.00)[100.00%] Received-SPF: pass client-ip=195.135.220.29; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Bring back the 'ready' semaphore, but this time make it per-channel, so that we can do true lockstep switching of MultiFDPages without taking the channel lock. Drop the channel lock as it now becomes useless. The rules for accessing the MultiFDSendParams are: - between sem and sem_done/ready if we're the channel qemu_sem_post(&p->ready); qemu_sem_wait(&p->sem); qemu_sem_post(&p->sem_done); - between ready and sem if we're not the channel qemu_sem_wait(&p->ready); qemu_sem_post(&p->sem); Signed-off-by: Fabiano Rosas --- One issue I can see with this is that we might now have to wait at multifd_send_pages() if a channel takes too long to send it's packet and come back to p->ready. We would need to find a way of ignoring a slow channel and skipping ahead to the next one in line. --- migration/multifd.c | 45 +++++++++++++-------------------------------- migration/multifd.h | 5 ++--- 2 files changed, 15 insertions(+), 35 deletions(-) diff --git a/migration/multifd.c b/migration/multifd.c index b7ba3fe0e6..7fa7bc33fd 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -410,10 +410,10 @@ static int multifd_send_pages(QEMUFile *f) for (i = next_channel;; i = (i + 1) % migrate_multifd_channels()) { p = &multifd_send_state->params[i]; - qemu_mutex_lock(&p->mutex); + qemu_sem_wait(&p->ready); + if (p->quit) { error_report("%s: channel %d has already quit!", __func__, i); - qemu_mutex_unlock(&p->mutex); return -1; } if (!p->pending_job) { @@ -421,7 +421,6 @@ static int multifd_send_pages(QEMUFile *f) next_channel = (i + 1) % migrate_multifd_channels(); break; } - qemu_mutex_unlock(&p->mutex); } assert(!p->pages->num); assert(!p->pages->block); @@ -429,7 +428,6 @@ static int multifd_send_pages(QEMUFile *f) p->packet_num = multifd_send_state->packet_num++; multifd_send_state->pages = p->pages; p->pages = pages; - qemu_mutex_unlock(&p->mutex); qemu_sem_post(&p->sem); return 1; @@ -529,9 +527,9 @@ void multifd_save_cleanup(void) } socket_send_channel_destroy(p->c); p->c = NULL; - qemu_mutex_destroy(&p->mutex); qemu_sem_destroy(&p->sem); qemu_sem_destroy(&p->sem_done); + qemu_sem_destroy(&p->ready); g_free(p->name); p->name = NULL; multifd_pages_clear(p->pages); @@ -586,14 +584,12 @@ static void multifd_send_wait(void) * Even idle channels will wait for p->sem at the top of the * loop. */ + qemu_sem_wait(&p->ready); qemu_sem_post(&p->sem); trace_multifd_send_wait(migrate_multifd_channels() - i); qemu_sem_wait(&p->sem_done); - - qemu_mutex_lock(&p->mutex); assert(!p->pending_job || p->quit); - qemu_mutex_unlock(&p->mutex); } /* @@ -621,20 +617,17 @@ int multifd_send_sync_main(QEMUFile *f) for (i = 0; i < migrate_multifd_channels(); i++) { MultiFDSendParams *p = &multifd_send_state->params[i]; + qemu_sem_wait(&p->ready); trace_multifd_send_sync_main_signal(p->id); - qemu_mutex_lock(&p->mutex); - if (p->quit) { error_report("%s: channel %d has already quit", __func__, i); - qemu_mutex_unlock(&p->mutex); return -1; } p->packet_num = multifd_send_state->packet_num++; p->flags |= MULTIFD_FLAG_SYNC; p->pending_job++; - qemu_mutex_unlock(&p->mutex); qemu_sem_post(&p->sem); } @@ -685,15 +678,14 @@ static void *multifd_send_thread(void *opaque) p->num_packets = 1; while (true) { + qemu_sem_post(&p->ready); qemu_sem_wait(&p->sem); if (qatomic_read(&multifd_send_state->exiting)) { - qemu_mutex_lock(&p->mutex); p->quit = true; - qemu_mutex_unlock(&p->mutex); + qemu_sem_post(&p->sem_done); break; } - qemu_mutex_lock(&p->mutex); if (p->pending_job) { uint64_t packet_num = p->packet_num; @@ -714,7 +706,6 @@ static void *multifd_send_thread(void *opaque) if (p->normal_num) { ret = multifd_send_state->ops->send_prepare(p, &local_err); if (ret != 0) { - qemu_mutex_unlock(&p->mutex); break; } } @@ -725,7 +716,6 @@ static void *multifd_send_thread(void *opaque) p->total_normal_pages += p->normal_num; p->pages->num = 0; p->pages->block = NULL; - qemu_mutex_unlock(&p->mutex); trace_multifd_send(p->id, packet_num, p->normal_num, flags, p->next_packet_size); @@ -753,12 +743,9 @@ static void *multifd_send_thread(void *opaque) stat64_add(&mig_stats.multifd_bytes, p->next_packet_size); stat64_add(&mig_stats.transferred, p->next_packet_size); - qemu_mutex_lock(&p->mutex); p->pending_job--; - qemu_mutex_unlock(&p->mutex); } else { - qemu_mutex_unlock(&p->mutex); qemu_sem_post(&p->sem_done); } } @@ -766,11 +753,8 @@ static void *multifd_send_thread(void *opaque) out: if (local_err) { trace_multifd_send_error(p->id); - - qemu_mutex_lock(&p->mutex); p->quit = true; - qemu_mutex_unlock(&p->mutex); - + qemu_sem_post(&p->ready); multifd_send_terminate_threads(local_err); error_free(local_err); } @@ -780,12 +764,10 @@ out: * who pay attention to me. */ if (ret != 0) { - qemu_sem_post(&p->sem_done); + p->quit = true; + qemu_sem_post(&p->ready); } - - qemu_mutex_lock(&p->mutex); p->running = false; - qemu_mutex_unlock(&p->mutex); rcu_unregister_thread(); migration_threads_remove(thread); @@ -817,7 +799,7 @@ static void multifd_tls_outgoing_handshake(QIOTask *task, * is not created, and then tell who pay attention to me. */ p->quit = true; - qemu_sem_post(&p->sem_done); + qemu_sem_post(&p->ready); } } @@ -893,14 +875,13 @@ static void multifd_new_send_channel_cleanup(MultiFDSendParams *p, QIOChannel *ioc, Error *err) { migrate_set_error(migrate_get_current(), err); - /* Error happen, we need to tell who pay attention to me */ - qemu_sem_post(&p->sem_done); /* * Although multifd_send_thread is not created, but main migration * thread need to judge whether it is running, so we need to mark * its status. */ p->quit = true; + qemu_sem_post(&p->ready); object_unref(OBJECT(ioc)); error_free(err); } @@ -944,9 +925,9 @@ int multifd_save_setup(Error **errp) for (i = 0; i < thread_count; i++) { MultiFDSendParams *p = &multifd_send_state->params[i]; - qemu_mutex_init(&p->mutex); qemu_sem_init(&p->sem, 0); qemu_sem_init(&p->sem_done, 0); + qemu_sem_init(&p->ready, 0); p->quit = false; p->pending_job = 0; p->id = i; diff --git a/migration/multifd.h b/migration/multifd.h index 71bd66974d..6bb10b07aa 100644 --- a/migration/multifd.h +++ b/migration/multifd.h @@ -93,8 +93,8 @@ typedef struct { /* channel is done transmitting until more pages are queued */ QemuSemaphore sem_done; - /* this mutex protects the following parameters */ - QemuMutex mutex; + QemuSemaphore ready; + /* is this channel thread running */ bool running; /* should this thread finish */ @@ -209,4 +209,3 @@ typedef struct { void multifd_register_ops(int method, MultiFDMethods *ops); #endif -