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Mon, 29 Jan 2024 12:42:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Tcb5ATOdt2UnHQAAD6G6ig (envelope-from ); Mon, 29 Jan 2024 12:42:27 +0000 From: Fabiano Rosas To: Peter Xu Cc: qemu-devel@nongnu.org, Hao Xiang , Yuan Liu , Bryan Zhang , Avihai Horon Subject: Re: [PATCH 1/5] migration/multifd: Separate compression ops from non-compression In-Reply-To: References: <20240126221943.26628-1-farosas@suse.de> <20240126221943.26628-2-farosas@suse.de> Date: Mon, 29 Jan 2024 09:42:24 -0300 Message-ID: <87mssoe2fj.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=ktllmi0L; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=a6Gbjhij X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-4.51 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; BAYES_HAM(-3.00)[100.00%]; MIME_GOOD(-0.10)[text/plain]; NEURAL_HAM_LONG(-1.00)[-1.000]; RCPT_COUNT_FIVE(0.00)[6]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+]; MX_GOOD(-0.01)[]; NEURAL_HAM_SHORT(-0.20)[-0.999]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[] X-Rspamd-Queue-Id: BC28222037 Received-SPF: pass client-ip=195.135.223.130; envelope-from=farosas@suse.de; helo=smtp-out1.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, 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 Peter Xu writes: > On Fri, Jan 26, 2024 at 07:19:39PM -0300, Fabiano Rosas wrote: >> +static MultiFDMethods multifd_socket_ops = { >> + .send_setup = multifd_socket_send_setup, >> + .send_cleanup = multifd_socket_send_cleanup, >> + .send_prepare = multifd_socket_send_prepare, > > Here it's named with "socket", however not all socket-based multifd > migrations will go into this route, e.g., when zstd compression enabled it > will not go via this route, even if zstd also uses sockets as transport. > From that pov, this may be slightly confusing. Maybe it suites more to be > called "socket_plain" / "socket_no_comp"? > > One step back, I had a feeling that the current proposal tried to provide a > single ->ops to cover a model where we may need more than one layer of > abstraction. > > Since it might be helpful to allow multifd send arbitrary data (e.g. for > VFIO? Avihai might have an answer there..), I'll try to even consider that > into the picture. > > Let's consider the ultimate goal of multifd, where the simplest model could > look like this in my mind (I'm only discussing sender side, but it'll be > similar on recv side): > > prepare() send() > Input ----------------> IOVs ------------> iochannels > > [I used prepare/send, but please think them as generic terms, not 100% > aligned with what we have with existing multifd_ops, or what you proposed > later] > > Here what are sure, IMHO, is: > > - We always can have some input data to dump; I didn't use "guest pages" > just to say we may allow arbitrary data. For any multifd user that > would like to dump arbitrary data, they can already provide IOVs, so > here input can be either "MultiFDPages_t" or "IOVs". Or anything else, since the client code also has control over send(), no? So it could give multifd a pointer to some memory and then use send() to do whatever it wants with it. Multifd is just providing worker threads and "scheduling". Also note that multifd clients currently _do not_ provide IOVs. They merely provide data to multifd (p->pages) and then convert that data into IOVs at prepare(). This is different, because multifd currently holds that p->pages (and turns that into p->normal), which means the client code does not need to store the data across iterations (in the case of RAM which is iterative). > > - We may always want to have IOVs to represent the buffers at some point, > no matter what the input it > > - We always flush the IOVs to iochannels; basically I want to say we can > always assume the last layer is connecting to QIOChannel APIs, while I > don't think there's outliers here so far, even if the send() may differ. > > Then _maybe_ it's clearer that we can have two layers of OPs? > > - prepare(): it tells how the "input" will be converted into a scatter > gatter list of buffers. All compression methods fall into this afaiu. > This has _nothing_ to do on how the buffers will be sent. For > arbitrary-typed input, this can already be a no-op since the IOVs > provided can already be passed over to send(). > > - send(): how to dump the IOVs to the iochannels. AFAIU this is motly > only useful for fixed-ram migrations. > > Would this be clearer, rather than keep using a single multifd_ops? Sorry, I don't see how what you describe is any different than what we have. And I don't see how any of this would mean more than one multifd_ops. We already have multifd_ops->prepare() and multifd_ops->send(). What am I missing?