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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id o3-20020a05600c4fc300b0037bea2f9775sm2286073wmq.25.2022.02.22.03.32.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Feb 2022 03:32:12 -0800 (PST) Date: Tue, 22 Feb 2022 11:32:10 +0000 From: "Dr. David Alan Gilbert" To: Peter Xu Subject: Re: [PATCH 19/20] migration: Postcopy recover with preempt enabled Message-ID: References: <20220216062809.57179-1-peterx@redhat.com> <20220216062809.57179-20-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220216062809.57179-20-peterx@redhat.com> User-Agent: Mutt/2.1.5 (2021-12-30) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Cc: Leonardo Bras Soares Passos , qemu-devel@nongnu.org, Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Xu (peterx@redhat.com) wrote: > To allow postcopy recovery, the ram fast load (preempt-only) dest QEMU thread > needs similar handling on fault tolerance. When ram_load_postcopy() fails, > instead of stopping the thread it halts with a semaphore, preparing to be > kicked again when recovery is detected. > > A mutex is introduced to make sure there's no concurrent operation upon the > socket. To make it simple, the fast ram load thread will take the mutex during > its whole procedure, and only release it if it's paused. The fast-path socket > will be properly released by the main loading thread safely when there's > network failures during postcopy with that mutex held. I *think* this is mostly OK; but I worry I don't understand all the cases; e.g. a) If the postcopy channel errors first b) If the main channel errors first Can you add some docs to walk through those and explain the locking ? Dave > Signed-off-by: Peter Xu > --- > migration/migration.c | 17 +++++++++++++++-- > migration/migration.h | 3 +++ > migration/postcopy-ram.c | 24 ++++++++++++++++++++++-- > migration/savevm.c | 17 +++++++++++++++++ > migration/trace-events | 2 ++ > 5 files changed, 59 insertions(+), 4 deletions(-) > > diff --git a/migration/migration.c b/migration/migration.c > index d20db04097..c68a281406 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -215,9 +215,11 @@ void migration_object_init(void) > current_incoming->postcopy_remote_fds = > g_array_new(FALSE, TRUE, sizeof(struct PostCopyFD)); > qemu_mutex_init(¤t_incoming->rp_mutex); > + qemu_mutex_init(¤t_incoming->postcopy_prio_thread_mutex); > qemu_event_init(¤t_incoming->main_thread_load_event, false); > qemu_sem_init(¤t_incoming->postcopy_pause_sem_dst, 0); > qemu_sem_init(¤t_incoming->postcopy_pause_sem_fault, 0); > + qemu_sem_init(¤t_incoming->postcopy_pause_sem_fast_load, 0); > qemu_mutex_init(¤t_incoming->page_request_mutex); > current_incoming->page_requested = g_tree_new(page_request_addr_cmp); > > @@ -697,9 +699,9 @@ static bool postcopy_try_recover(void) > > /* > * Here, we only wake up the main loading thread (while the > - * fault thread will still be waiting), so that we can receive > + * rest threads will still be waiting), so that we can receive > * commands from source now, and answer it if needed. The > - * fault thread will be woken up afterwards until we are sure > + * rest threads will be woken up afterwards until we are sure > * that source is ready to reply to page requests. > */ > qemu_sem_post(&mis->postcopy_pause_sem_dst); > @@ -3466,6 +3468,17 @@ static MigThrError postcopy_pause(MigrationState *s) > qemu_file_shutdown(file); > qemu_fclose(file); > > + /* > + * Do the same to postcopy fast path socket too if there is. No > + * locking needed because no racer as long as we do this before setting > + * status to paused. > + */ > + if (s->postcopy_qemufile_src) { > + migration_ioc_unregister_yank_from_file(s->postcopy_qemufile_src); Shouldn't this do a qemu_file_shutdown on here first? > + qemu_fclose(s->postcopy_qemufile_src); > + s->postcopy_qemufile_src = NULL; > + } > + > migrate_set_state(&s->state, s->state, > MIGRATION_STATUS_POSTCOPY_PAUSED); > > diff --git a/migration/migration.h b/migration/migration.h > index b8aacfe3af..945088064a 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -118,6 +118,8 @@ struct MigrationIncomingState { > /* Postcopy priority thread is used to receive postcopy requested pages */ > QemuThread postcopy_prio_thread; > bool postcopy_prio_thread_created; > + /* Used to sync with the prio thread */ > + QemuMutex postcopy_prio_thread_mutex; > /* > * An array of temp host huge pages to be used, one for each postcopy > * channel. > @@ -147,6 +149,7 @@ struct MigrationIncomingState { > /* notify PAUSED postcopy incoming migrations to try to continue */ > QemuSemaphore postcopy_pause_sem_dst; > QemuSemaphore postcopy_pause_sem_fault; > + QemuSemaphore postcopy_pause_sem_fast_load; > > /* List of listening socket addresses */ > SocketAddressList *socket_address_list; > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index 30eddaacd1..b3d23804bc 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -1575,6 +1575,15 @@ int postcopy_preempt_setup(MigrationState *s, Error **errp) > return 0; > } > > +static void postcopy_pause_ram_fast_load(MigrationIncomingState *mis) > +{ > + trace_postcopy_pause_fast_load(); > + qemu_mutex_unlock(&mis->postcopy_prio_thread_mutex); > + qemu_sem_wait(&mis->postcopy_pause_sem_fast_load); > + qemu_mutex_lock(&mis->postcopy_prio_thread_mutex); > + trace_postcopy_pause_fast_load_continued(); > +} > + > void *postcopy_preempt_thread(void *opaque) > { > MigrationIncomingState *mis = opaque; > @@ -1587,11 +1596,22 @@ void *postcopy_preempt_thread(void *opaque) > qemu_sem_post(&mis->thread_sync_sem); > > /* Sending RAM_SAVE_FLAG_EOS to terminate this thread */ > - ret = ram_load_postcopy(mis->postcopy_qemufile_dst, RAM_CHANNEL_POSTCOPY); > + qemu_mutex_lock(&mis->postcopy_prio_thread_mutex); > + while (1) { > + ret = ram_load_postcopy(mis->postcopy_qemufile_dst, RAM_CHANNEL_POSTCOPY); > + /* If error happened, go into recovery routine */ > + if (ret) { > + postcopy_pause_ram_fast_load(mis); > + } else { > + /* We're done */ > + break; > + } > + } > + qemu_mutex_unlock(&mis->postcopy_prio_thread_mutex); > > rcu_unregister_thread(); > > trace_postcopy_preempt_thread_exit(); > > - return ret == 0 ? NULL : (void *)-1; > + return NULL; > } > diff --git a/migration/savevm.c b/migration/savevm.c > index 254aa78234..2d32340d28 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -2152,6 +2152,13 @@ static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis) > */ > qemu_sem_post(&mis->postcopy_pause_sem_fault); > > + if (migrate_postcopy_preempt()) { > + /* The channel should already be setup again; make sure of it */ > + assert(mis->postcopy_qemufile_dst); > + /* Kick the fast ram load thread too */ > + qemu_sem_post(&mis->postcopy_pause_sem_fast_load); > + } > + > return 0; > } > > @@ -2607,6 +2614,16 @@ static bool postcopy_pause_incoming(MigrationIncomingState *mis) > mis->to_src_file = NULL; > qemu_mutex_unlock(&mis->rp_mutex); > > + if (mis->postcopy_qemufile_dst) { > + qemu_file_shutdown(mis->postcopy_qemufile_dst); > + /* Take the mutex to make sure the fast ram load thread halted */ > + qemu_mutex_lock(&mis->postcopy_prio_thread_mutex); > + migration_ioc_unregister_yank_from_file(mis->postcopy_qemufile_dst); > + qemu_fclose(mis->postcopy_qemufile_dst); > + mis->postcopy_qemufile_dst = NULL; > + qemu_mutex_unlock(&mis->postcopy_prio_thread_mutex); > + } > + > migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_ACTIVE, > MIGRATION_STATUS_POSTCOPY_PAUSED); > > diff --git a/migration/trace-events b/migration/trace-events > index b1155d9da0..dfe36a3340 100644 > --- a/migration/trace-events > +++ b/migration/trace-events > @@ -270,6 +270,8 @@ mark_postcopy_blocktime_begin(uint64_t addr, void *dd, uint32_t time, int cpu, i > mark_postcopy_blocktime_end(uint64_t addr, void *dd, uint32_t time, int affected_cpu) "addr: 0x%" PRIx64 ", dd: %p, time: %u, affected_cpu: %d" > postcopy_pause_fault_thread(void) "" > postcopy_pause_fault_thread_continued(void) "" > +postcopy_pause_fast_load(void) "" > +postcopy_pause_fast_load_continued(void) "" > postcopy_ram_fault_thread_entry(void) "" > postcopy_ram_fault_thread_exit(void) "" > postcopy_ram_fault_thread_fds_core(int baseufd, int quitfd) "ufd: %d quitfd: %d" > -- > 2.32.0 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK