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h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=++Is/2mFziUP/EUP+aPGrjXPSq6ScRThkQMj6DrB2oc=; b=iUS/ly2k+F/WDgx53vDoj2n0UdPzCP5IBI+aLLr6ZSm4hT0PkQaiJwPoMsNEX+vDFx0c/F HWO8QXpQ+S6HM+L4JQmpwFggE7ijpxjocscSU1odFg4oqSF8ldu4x6rJaTdGlYY+iO879v S6nOBBo+68TfdQufVmyGa79Y5hKDVII= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1697119626; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=++Is/2mFziUP/EUP+aPGrjXPSq6ScRThkQMj6DrB2oc=; b=PYRFIJYyjc7uzhJaC+II9ppeRcUNG01hju5QCwdKQ073iwRHa3liinWhGtFg6NwbFmH/H/ YxbgfGkteLisggCg== 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 Content-Transfer-Encoding: quoted-printable Authentication-Results: smtp-out2.suse.de; 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charset="utf-8" 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 =3D next_channel;; i =3D (i + 1) % migrate_multifd_channels()) { p =3D &multifd_send_state->params[i]; =20 - 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 =3D (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 =3D multifd_send_state->packet_num++; multifd_send_state->pages =3D p->pages; p->pages =3D pages; - qemu_mutex_unlock(&p->mutex); qemu_sem_post(&p->sem); =20 return 1; @@ -529,9 +527,9 @@ void multifd_save_cleanup(void) } socket_send_channel_destroy(p->c); p->c =3D 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 =3D 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); =20 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); } =20 /* @@ -621,20 +617,17 @@ int multifd_send_sync_main(QEMUFile *f) for (i =3D 0; i < migrate_multifd_channels(); i++) { MultiFDSendParams *p =3D &multifd_send_state->params[i]; =20 + qemu_sem_wait(&p->ready); trace_multifd_send_sync_main_signal(p->id); =20 - 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; } =20 p->packet_num =3D multifd_send_state->packet_num++; p->flags |=3D MULTIFD_FLAG_SYNC; p->pending_job++; - qemu_mutex_unlock(&p->mutex); qemu_sem_post(&p->sem); } =20 @@ -685,15 +678,14 @@ static void *multifd_send_thread(void *opaque) p->num_packets =3D 1; =20 while (true) { + qemu_sem_post(&p->ready); qemu_sem_wait(&p->sem); =20 if (qatomic_read(&multifd_send_state->exiting)) { - qemu_mutex_lock(&p->mutex); p->quit =3D true; - qemu_mutex_unlock(&p->mutex); + qemu_sem_post(&p->sem_done); break; } - qemu_mutex_lock(&p->mutex); =20 if (p->pending_job) { uint64_t packet_num =3D p->packet_num; @@ -714,7 +706,6 @@ static void *multifd_send_thread(void *opaque) if (p->normal_num) { ret =3D multifd_send_state->ops->send_prepare(p, &local_er= r); if (ret !=3D 0) { - qemu_mutex_unlock(&p->mutex); break; } } @@ -725,7 +716,6 @@ static void *multifd_send_thread(void *opaque) p->total_normal_pages +=3D p->normal_num; p->pages->num =3D 0; p->pages->block =3D NULL; - qemu_mutex_unlock(&p->mutex); =20 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) =20 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); =20 } 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 =3D 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 !=3D 0) { - qemu_sem_post(&p->sem_done); + p->quit =3D true; + qemu_sem_post(&p->ready); } - - qemu_mutex_lock(&p->mutex); p->running =3D false; - qemu_mutex_unlock(&p->mutex); =20 rcu_unregister_thread(); migration_threads_remove(thread); @@ -817,7 +799,7 @@ static void multifd_tls_outgoing_handshake(QIOTask *tas= k, * is not created, and then tell who pay attention to me. */ p->quit =3D true; - qemu_sem_post(&p->sem_done); + qemu_sem_post(&p->ready); } } =20 @@ -893,14 +875,13 @@ static void multifd_new_send_channel_cleanup(MultiFDS= endParams *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 =3D 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 =3D 0; i < thread_count; i++) { MultiFDSendParams *p =3D &multifd_send_state->params[i]; =20 - 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 =3D false; p->pending_job =3D 0; p->id =3D 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; =20 - /* 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); =20 #endif - --=20 2.35.3