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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-454fe1b7d2asm54444531cf.93.2024.08.27.12.09.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Aug 2024 12:09:33 -0700 (PDT) Date: Tue, 27 Aug 2024 15:09:31 -0400 From: Peter Xu To: Fabiano Rosas Cc: qemu-devel@nongnu.org, "Maciej S . Szmigiero" , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH v6 19/19] migration/multifd: Add documentation for multifd methods Message-ID: References: <20240827174606.10352-1-farosas@suse.de> <20240827174606.10352-20-farosas@suse.de> <87mskxx0ck.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87mskxx0ck.fsf@suse.de> Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Aug 27, 2024 at 03:54:51PM -0300, Fabiano Rosas wrote: > Peter Xu writes: > > > On Tue, Aug 27, 2024 at 02:46:06PM -0300, Fabiano Rosas wrote: > >> Add documentation clarifying the usage of the multifd methods. The > >> general idea is that the client code calls into multifd to trigger > >> send/recv of data and multifd then calls these hooks back from the > >> worker threads at opportune moments so the client can process a > >> portion of the data. > >> > >> Suggested-by: Peter Xu > >> Signed-off-by: Fabiano Rosas > >> --- > >> Note that the doc is not symmetrical among send/recv because the recv > >> side is still wonky. It doesn't give the packet to the hooks, which > >> forces the p->normal, p->zero, etc. to be processed at the top level > >> of the threads, where no client-specific information should be. > >> --- > >> migration/multifd.h | 76 +++++++++++++++++++++++++++++++++++++++++---- > >> 1 file changed, 70 insertions(+), 6 deletions(-) > >> > >> diff --git a/migration/multifd.h b/migration/multifd.h > >> index 13e7a88c01..ebb17bdbcf 100644 > >> --- a/migration/multifd.h > >> +++ b/migration/multifd.h > >> @@ -229,17 +229,81 @@ typedef struct { > >> } MultiFDRecvParams; > >> > >> typedef struct { > >> - /* Setup for sending side */ > >> + /* > >> + * The send_setup, send_cleanup, send_prepare are only called on > >> + * the QEMU instance at the migration source. > >> + */ > >> + > >> + /* > >> + * Setup for sending side. Called once per channel during channel > >> + * setup phase. > >> + * > >> + * Must allocate p->iov. If packets are in use (default), one > > > > Pure thoughts: wonder whether we can assert(p->iov) that after the hook > > returns in code to match this line. > > Not worth the extra instructions in my opinion. It would crash > immediately once the thread touches p->iov anyway. It might still be good IMHO to have that assert(), not only to abort earlier, but also as a code-styled comment. Your call when resend. PS: feel free to queue existing patches into your own tree without resending the whole series! > > > > >> + * extra iovec must be allocated for the packet header. Any memory > >> + * allocated in this hook must be released at send_cleanup. > >> + * > >> + * p->write_flags may be used for passing flags to the QIOChannel. > >> + * > >> + * p->compression_data may be used by compression methods to store > >> + * compression data. > >> + */ > >> int (*send_setup)(MultiFDSendParams *p, Error **errp); > >> - /* Cleanup for sending side */ > >> + > >> + /* > >> + * Cleanup for sending side. Called once per channel during > >> + * channel cleanup phase. May be empty. > > > > Hmm, if we require p->iov allocation per-ops, then they must free it here? > > I wonder whether we leaked it in most compressors. > > Sorry, this one shouldn't have that text. I still want to double check with you: we leaked iov[] in most compressors here, or did I overlook something? That's definitely more important than the doc update itself.. > > > > > With that, I wonder whether we should also assert(p->iov == NULL) after > > this one returns (squash in this same patch). > > > >> + */ > >> void (*send_cleanup)(MultiFDSendParams *p, Error **errp); > >> - /* Prepare the send packet */ > >> + > >> + /* > >> + * Prepare the send packet. Called from multifd_send(), with p > > > > multifd_send_thread()? > > No, I meant called as a result of multifd_send(), which is the function > the client uses to trigger a send on the thread. OK, but it's confusing. Some rewords you mentioned below could work. > > > > >> + * pointing to the MultiFDSendParams of a channel that is > >> + * currently idle. > >> + * > >> + * Must populate p->iov with the data to be sent, increment > >> + * p->iovs_num to match the amount of iovecs used and set > >> + * p->next_packet_size with the amount of data currently present > >> + * in p->iov. > >> + * > >> + * Must indicate whether this is a compression packet by setting > >> + * p->flags. > > > > Sigh.. I wonder whether we could avoid mentioning this, and also we avoid > > adding new flags for new compressors, relying on libvirt guarding things. > > Then when we have the handshakes that's something we verify there. > > > > I understand that part is not in the best shape, but we must document > the current state. There's no problem changing this later. > > Besides, there's the whole "the migration stream should be considered > hostile" which might mean we should really be keeping these sanity check > flags around in case something really weird happens so we don't carry on > with a bad stream. Yep, it's OK. > > >> + * > >> + * As a last step, if packets are in use (default), must prepare > >> + * the packet by calling multifd_send_fill_packet(). > >> + */ > >> int (*send_prepare)(MultiFDSendParams *p, Error **errp); > >> - /* Setup for receiving side */ > >> + > >> + /* > >> + * The recv_setup, recv_cleanup, recv are only called on the QEMU > >> + * instance at the migration destination. > >> + */ > >> + > >> + /* > >> + * Setup for receiving side. Called once per channel during > >> + * channel setup phase. May be empty. > >> + * > >> + * May allocate data structures for the receiving of data. May use > >> + * p->iov. Compression methods may use p->compress_data. > >> + */ > >> int (*recv_setup)(MultiFDRecvParams *p, Error **errp); > >> - /* Cleanup for receiving side */ > >> + > >> + /* > >> + * Cleanup for receiving side. Called once per channel during > >> + * channel cleanup phase. May be empty. > >> + */ > >> void (*recv_cleanup)(MultiFDRecvParams *p); > >> - /* Read all data */ > >> + > >> + /* > >> + * Data receive method. Called from multifd_recv(), with p > > > > multifd_recv_thread()? > > Same as before. I'll reword this somehow. > > > > >> + * pointing to the MultiFDRecvParams of a channel that is > >> + * currently idle. Only called if there is data available to > >> + * receive. > >> + * > >> + * Must validate p->flags according to what was set at > >> + * send_prepare. > >> + * > >> + * Must read the data from the QIOChannel p->c. > >> + */ > >> int (*recv)(MultiFDRecvParams *p, Error **errp); > >> } MultiFDMethods; > >> > >> -- > >> 2.35.3 > >> > -- Peter Xu