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Szmigiero" , Alex Williamson , Avihai Horon , =?utf-8?Q?C=C3=A9dric?= Le Goater Subject: Re: [PATCH 2/2] migration/multifd: Allow to sync with sender threads only In-Reply-To: <20241205185303.897010-3-peterx@redhat.com> References: <20241205185303.897010-1-peterx@redhat.com> <20241205185303.897010-3-peterx@redhat.com> Date: Thu, 05 Dec 2024 17:16:05 -0300 Message-ID: <875xnxj37e.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 1DEAB1F393 X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_HAS_DN(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; MISSING_XM_UA(0.00)[]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid, suse.de:dkim, imap1.dmz-prg2.suse.org:rdns, imap1.dmz-prg2.suse.org:helo] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org Received-SPF: pass client-ip=195.135.223.131; 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, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Xu writes: > Teach multifd_send_sync_main() to sync with threads only. > > We already have such requests, which is when mapped-ram is enabled with > multifd. In that case, no SYNC messages will be pushed to the stream when > multifd syncs the sender threads because there's no destination threads > waiting for that. The whole point of the sync is to make sure all threads > flushed their jobs. > > So fundamentally we have a request to do the sync in different ways: > > - Either to sync the threads only, > - Or to sync the threads but also with the destination side > > Mapped-ram did it already because of the use_packet check in the sync > handler of the sender thread. It works. > > However it may stop working when e.g. VFIO may start to reuse multifd > channels to push device states. In that case VFIO has similar request on > "thread-only sync" however we can't check a flag because such sync request > can still come from RAM which needs the on-wire notifications. > > Paving way for that by allowing the multifd_send_sync_main() to specify > what kind of sync the caller needs. We can use it for mapped-ram already. > > No functional change intended. > > Signed-off-by: Peter Xu > --- > migration/multifd.h | 16 +++++++++++++--- > migration/multifd-nocomp.c | 8 +++++++- > migration/multifd.c | 14 ++++++++------ > 3 files changed, 28 insertions(+), 10 deletions(-) > > diff --git a/migration/multifd.h b/migration/multifd.h > index 50d58c0c9c..6b2f60a917 100644 > --- a/migration/multifd.h > +++ b/migration/multifd.h > @@ -19,6 +19,15 @@ > typedef struct MultiFDRecvData MultiFDRecvData; > typedef struct MultiFDSendData MultiFDSendData; > > +typedef enum { > + /* No sync request */ > + MULTIFD_SYNC_NONE = 0, > + /* Sync on the sender threads without pushing messages */ > + MULTIFD_SYNC_THREADS, > + /* Sync on the sender threads, meanwhile push "SYNC" message to the wire */ s/meanwhile// > + MULTIFD_SYNC_THREADS_AND_NOTIFY, > +} MultiFDSyncReq; I think I'd prefer the local vs. remote terminology I introduced in my proposal [1] for cleaning up the multifd_flush_after_each_section() code: LOCAL - sync the local threads between themselves REMOTE - put a message on the stream for the remote end to perform a sync on their threads. Down below you're passing the MULTIFD_SYNC_THREADS_AND_NOTIFY into the send thread, but the "sync threads" part of this is really done outside the thread, so that part doesn't have a meaning inside the thread. 1- https://lore.kernel.org/r/875xo8n4ue.fsf@suse.de Also, please provide your input there^, it would be nice to unify the terminology and reasoning about both changes. > + > bool multifd_send_setup(void); > void multifd_send_shutdown(void); > void multifd_send_channel_created(void); > @@ -28,7 +37,7 @@ void multifd_recv_shutdown(void); > bool multifd_recv_all_channels_created(void); > void multifd_recv_new_channel(QIOChannel *ioc, Error **errp); > void multifd_recv_sync_main(void); > -int multifd_send_sync_main(void); > +int multifd_send_sync_main(MultiFDSyncReq req); > bool multifd_queue_page(RAMBlock *block, ram_addr_t offset); > bool multifd_recv(void); > MultiFDRecvData *multifd_get_recv_data(void); > @@ -143,7 +152,7 @@ typedef struct { > /* multifd flags for each packet */ > uint32_t flags; > /* > - * The sender thread has work to do if either of below boolean is set. > + * The sender thread has work to do if either of below field is set. > * > * @pending_job: a job is pending > * @pending_sync: a sync request is pending > @@ -152,7 +161,8 @@ typedef struct { > * cleared by the multifd sender threads. > */ > bool pending_job; > - bool pending_sync; > + MultiFDSyncReq pending_sync; > + > MultiFDSendData *data; > > /* thread local variables. No locking required */ > diff --git a/migration/multifd-nocomp.c b/migration/multifd-nocomp.c > index 55191152f9..f64c4c9abd 100644 > --- a/migration/multifd-nocomp.c > +++ b/migration/multifd-nocomp.c > @@ -345,6 +345,8 @@ retry: > > int multifd_ram_flush_and_sync(void) > { > + MultiFDSyncReq req; > + > if (!migrate_multifd()) { > return 0; > } > @@ -356,7 +358,11 @@ int multifd_ram_flush_and_sync(void) > } > } > > - return multifd_send_sync_main(); > + /* File migrations only need to sync with threads */ > + req = migrate_mapped_ram() ? > + MULTIFD_SYNC_THREADS : MULTIFD_SYNC_THREADS_AND_NOTIFY; > + > + return multifd_send_sync_main(req); > } > > bool multifd_send_prepare_common(MultiFDSendParams *p) > diff --git a/migration/multifd.c b/migration/multifd.c > index 498e71fd10..77645e87a0 100644 > --- a/migration/multifd.c > +++ b/migration/multifd.c > @@ -523,7 +523,7 @@ static int multifd_zero_copy_flush(QIOChannel *c) > return ret; > } > > -int multifd_send_sync_main(void) > +int multifd_send_sync_main(MultiFDSyncReq req) > { > int i; > bool flush_zero_copy; > @@ -543,8 +543,8 @@ int multifd_send_sync_main(void) > * We should be the only user so far, so not possible to be set by > * others concurrently. > */ > - assert(qatomic_read(&p->pending_sync) == false); > - qatomic_set(&p->pending_sync, true); > + assert(qatomic_read(&p->pending_sync) == MULTIFD_SYNC_NONE); > + qatomic_set(&p->pending_sync, req); Hmm, isn't it easier to skip the whole loop if req == MULTIFD_SYNC_THREADS? I don't remember why we kept this loop here for mapped-ram. > qemu_sem_post(&p->sem); > } > for (i = 0; i < migrate_multifd_channels(); i++) { > @@ -635,14 +635,16 @@ static void *multifd_send_thread(void *opaque) > */ > qatomic_store_release(&p->pending_job, false); > } else { > + MultiFDSyncReq req = qatomic_read(&p->pending_sync); > + > /* > * If not a normal job, must be a sync request. Note that > * pending_sync is a standalone flag (unlike pending_job), so > * it doesn't require explicit memory barriers. > */ > - assert(qatomic_read(&p->pending_sync)); > + assert(req != MULTIFD_SYNC_NONE); > > - if (use_packets) { > + if (req == MULTIFD_SYNC_THREADS_AND_NOTIFY) { Good, more explicit. > p->flags = MULTIFD_FLAG_SYNC; > multifd_send_fill_packet(p); > ret = qio_channel_write_all(p->c, (void *)p->packet, > @@ -654,7 +656,7 @@ static void *multifd_send_thread(void *opaque) > stat64_add(&mig_stats.multifd_bytes, p->packet_len); > } > > - qatomic_set(&p->pending_sync, false); > + qatomic_set(&p->pending_sync, MULTIFD_SYNC_NONE); It's a bit weird that MULTIFD_SYNC_THREADS will never have an use inside the thread. Makes me think it should never exist in the first place. But then we're back into pending_sync + use_packets... looks like it would be less convoluted to skip the loop up there and assert(!use_packets) in here. Unless I'm missing something... > qemu_sem_post(&p->sem_sync); > } > }