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Szmigiero" Subject: Re: [RFC PATCH v2 0/9] migration/multifd: Remove multifd_send_state->pages In-Reply-To: References: <20240722175914.24022-1-farosas@suse.de> <87msm9yy77.fsf@suse.de> Date: Mon, 22 Jul 2024 18:20:28 -0300 Message-ID: <87a5i9yvhf.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Spamd-Result: default: False [-1.10 / 50.00]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCPT_COUNT_THREE(0.00)[3] 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, 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 Mon, Jul 22, 2024 at 05:21:48PM -0300, Fabiano Rosas wrote: >> Peter Xu writes: >> >> > On Mon, Jul 22, 2024 at 02:59:05PM -0300, Fabiano Rosas wrote: >> >> Hi, >> >> >> >> In this v2 I took Peter's suggestion of keeping the channels' pointers >> >> and moving only the extra slot. The major changes are in patches 5 and >> >> 9. Patch 3 introduces the structure: >> >> >> >> typedef enum { >> >> MULTIFD_PAYLOAD_NONE, >> >> MULTIFD_PAYLOAD_RAM, >> >> } MultiFDPayloadType; >> >> >> >> struct MultiFDSendData { >> >> MultiFDPayloadType type; >> >> union { >> >> MultiFDPages_t ram; >> >> } u; >> >> }; >> >> >> >> I added a NONE type so we can use it to tell when the channel has >> >> finished sending a packet, since we'll need to switch types between >> >> clients anyway. This avoids having to introduce a 'size', or 'free' >> >> variable. >> > >> > This at least looks better to me, thanks. >> > >> >> >> >> WHAT'S MISSING: >> >> >> >> - The support for calling multifd_send() concurrently. Maciej has this >> >> in his series so I didn't touch it. >> >> >> >> - A way of adding methods for the new payload type. Currently, the >> >> compression methods are somewhat coupled with ram migration, so I'm >> >> not sure how to proceed. >> > >> > What is this one? Why compression methods need new payload? Aren't they >> > ram-typed? >> >> The data we transport is MultiFDPages_t, yes, but the MultiFDMethods are >> either nocomp, or the compression-specific methods >> (e.g. zlib_send_prepare). >> >> How do we add methods for the upcoming new payload types? I don't expect >> us to continue using nocomp and then do "if (ram)... else if >> (device_state) ..." inside of them. I would expect us to rename >> s/nocomp/ram/ and add a new set of MultiFDMethods for the new data type >> (e.g. vfio_send_prepare, vmstate_send_prepare, etc). >> >> multifd_nocomp_ops -> multifd_ram_ops // rename >> multifd_zlib_ops // existing >> multifd_device_ops // new >> >> The challenge here is that the current framework is nocomp >> vs. compression. It needs to become ram + compression vs. other types. > > IMHO we can keep multifd_ops[] only for RAM. There's only send_prepare() > that device state will need, and so far it's only (referring Maciej's > code): > > static int nocomp_send_prepare_device_state(MultiFDSendParams *p, > Error **errp) > { > multifd_send_prepare_header_device_state(p); > > assert(!(p->flags & MULTIFD_FLAG_SYNC)); > > p->next_packet_size = p->device_state->buf_len; > if (p->next_packet_size > 0) { > p->iov[p->iovs_num].iov_base = p->device_state->buf; > p->iov[p->iovs_num].iov_len = p->next_packet_size; > p->iovs_num++; > } > > p->flags |= MULTIFD_FLAG_NOCOMP | MULTIFD_FLAG_DEVICE_STATE; > > multifd_send_fill_packet_device_state(p); > > return 0; > } > > None of other multifd_ops are used. There's also a conditional around device_state when calling ->recv(). That could seems like it could go to a hook. https://lore.kernel.org/r/41dedaf2c9abebb5e45f88c052daa26320715a92.1718717584.git.maciej.szmigiero@oracle.com > > I think we can directly invoke this part of device state code in > multifd_send_thread() for now. So far I think it should be ok. It's not just that. There's also a check for "if (ram)" at every call to multifd_ops to avoid calling the ram code when doing the device migration. It would be way easier to just set noop functions for those. static MultiFDMethods multifd_devstate_ops = { .send_setup = noop_send_setup, .send_cleanup = noop_send_cleanup, .send_prepare = devstate_send_prepare, .recv_setup = noop_recv_setup, .recv_cleanup = noop_recv_cleanup, .recv = devstate_recv }; I'm not saying this needs to be done in this series though. But I do think that's the correct design choice for the long term.