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Szmigiero" , =?utf-8?Q?C=C3=A9dric?= Le Goater , Avihai Horon , Alex Williamson , Prasad Pandit Subject: Re: [PATCH v2 2/7] migration/multifd: Allow to sync with sender threads only In-Reply-To: References: <20241206005834.1050905-1-peterx@redhat.com> <20241206005834.1050905-3-peterx@redhat.com> <877c8dc58x.fsf@suse.de> Date: Fri, 06 Dec 2024 12:00:42 -0300 Message-ID: <87o71oc0v9.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: A882521111 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]; NEURAL_HAM_SHORT(-0.20)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:dkim]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org Received-SPF: pass client-ip=2a07:de40:b251:101:10:150:64:1; envelope-from=farosas@suse.de; helo=smtp-out1.suse.de X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, 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: > On Fri, Dec 06, 2024 at 10:26:06AM -0300, Fabiano Rosas wrote: >> 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. >> >> s/flushed/finished/ otherwise we risk confusing people. > > done. > >> >> > >> > 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 | 19 ++++++++++++++++--- >> > migration/multifd-nocomp.c | 7 ++++++- >> > migration/multifd.c | 15 +++++++++------ >> > 3 files changed, 31 insertions(+), 10 deletions(-) >> > >> > diff --git a/migration/multifd.h b/migration/multifd.h >> > index 50d58c0c9c..bd337631ec 100644 >> > --- a/migration/multifd.h >> > +++ b/migration/multifd.h >> > @@ -19,6 +19,18 @@ >> > typedef struct MultiFDRecvData MultiFDRecvData; >> > typedef struct MultiFDSendData MultiFDSendData; >> > >> > +typedef enum { >> > + /* No sync request */ >> > + MULTIFD_SYNC_NONE = 0, >> > + /* Sync locally on the sender threads without pushing messages */ >> > + MULTIFD_SYNC_LOCAL, >> > + /* >> > + * Sync not only on the sender threads, but also push "SYNC" message to >> > + * the wire (which is for a remote sync). >> >> s/SYNC/MULTIFD_FLAG_SYNC/ >> >> Do we need to also mention that this needs to be paired with a >> multifd_recv_sync_main() via the emission of the >> RAM_SAVE_FLAG_MULTIFD_FLUSH flag on the stream? > > If we want to mention something, IMO it would be better about what happens > on the src, not dest. It can be too hard to follow if we connect that > directly to the dest behavior. > > Does this look good to you? > > /* > * Sync not only on the sender threads, but also push MULTIFD_FLAG_SYNC > * message to the wire for each iochannel (which is for a remote sync). > * > * When remote sync is used, need to be paired with a follow up > * RAM_SAVE_FLAG_EOS / RAM_SAVE_FLAG_MULTIFD_FLUSH message on the main > * channel. > */ Yes, thanks.