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David Alan Gilbert" , peterx@redhat.com, Kevin Wolf , Paolo Bonzini , =?utf-8?Q?D?= =?utf-8?Q?aniel_P_=2E_Berrang=C3=A9?= , Hailiang Zhang , Yury Kotov , Vladimir Sementsov-Ogievskiy , Prasad Pandit , Zhang Chen , Li Zhijian , Juraj Marcin Subject: Re: [PATCH RFC 4/9] migration/rdma: Change io_create_watch() to return immediately In-Reply-To: <20250827205949.364606-5-peterx@redhat.com> References: <20250827205949.364606-1-peterx@redhat.com> <20250827205949.364606-5-peterx@redhat.com> Date: Tue, 16 Sep 2025 19:35:45 -0300 Message-ID: <87ms6uvxdq.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 174E61F387 X-Rspamd-Action: no action X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; 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)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[treblig.org,redhat.com,xfusion.com,yandex-team.ru,gmail.com,fujitsu.com]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,suse.de:mid]; URIBL_BLOCKED(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim,suse.de:mid]; DKIM_TRACE(0.00)[suse.de:+] Received-SPF: pass client-ip=2a07:de40:b251:101:10:150:64:2; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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: > The old RDMA's io_create_watch() isn't really doing much work anyway. For > G_IO_OUT, it already does return immediately. For G_IO_IN, it will try to > detect some RDMA context length however normally nobody will be able to set > it at all. > > Simplify the code so that RDMA iochannels simply always rely on synchronous > reads and writes. It is highly likely what 6ddd2d76ca6f86f was talking > about, that the async model isn't really working well. > > This helps because this is almost the only dependency that the migration > core would need a coroutine for rdma channels. > I don't understand this. How does this code require a coroutine? Isn't the io_watch exactly the strategy used when there is no coroutine? > Signed-off-by: Peter Xu > --- > migration/rdma.c | 69 +++--------------------------------------------- > 1 file changed, 3 insertions(+), 66 deletions(-) > > diff --git a/migration/rdma.c b/migration/rdma.c > index ed4e20b988..bcd7aae2f2 100644 > --- a/migration/rdma.c > +++ b/migration/rdma.c > @@ -2789,56 +2789,14 @@ static gboolean > qio_channel_rdma_source_prepare(GSource *source, > gint *timeout) > { > - QIOChannelRDMASource *rsource = (QIOChannelRDMASource *)source; > - RDMAContext *rdma; > - GIOCondition cond = 0; > *timeout = -1; > - > - RCU_READ_LOCK_GUARD(); > - if (rsource->condition == G_IO_IN) { > - rdma = qatomic_rcu_read(&rsource->rioc->rdmain); > - } else { > - rdma = qatomic_rcu_read(&rsource->rioc->rdmaout); > - } > - > - if (!rdma) { > - error_report("RDMAContext is NULL when prepare Gsource"); > - return FALSE; > - } > - > - if (rdma->wr_data[0].control_len) { > - cond |= G_IO_IN; > - } > - cond |= G_IO_OUT; > - > - return cond & rsource->condition; > + return TRUE; > } > > static gboolean > qio_channel_rdma_source_check(GSource *source) > { > - QIOChannelRDMASource *rsource = (QIOChannelRDMASource *)source; > - RDMAContext *rdma; > - GIOCondition cond = 0; > - > - RCU_READ_LOCK_GUARD(); > - if (rsource->condition == G_IO_IN) { > - rdma = qatomic_rcu_read(&rsource->rioc->rdmain); > - } else { > - rdma = qatomic_rcu_read(&rsource->rioc->rdmaout); > - } > - > - if (!rdma) { > - error_report("RDMAContext is NULL when check Gsource"); > - return FALSE; > - } > - > - if (rdma->wr_data[0].control_len) { > - cond |= G_IO_IN; > - } > - cond |= G_IO_OUT; > - > - return cond & rsource->condition; > + return TRUE; These are fine if we want the source to run as soon as possible, I think. But then... > } > > static gboolean > @@ -2848,29 +2806,8 @@ qio_channel_rdma_source_dispatch(GSource *source, > { > QIOChannelFunc func = (QIOChannelFunc)callback; > QIOChannelRDMASource *rsource = (QIOChannelRDMASource *)source; > - RDMAContext *rdma; > - GIOCondition cond = 0; > - > - RCU_READ_LOCK_GUARD(); > - if (rsource->condition == G_IO_IN) { > - rdma = qatomic_rcu_read(&rsource->rioc->rdmain); > - } else { > - rdma = qatomic_rcu_read(&rsource->rioc->rdmaout); > - } > - > - if (!rdma) { > - error_report("RDMAContext is NULL when dispatch Gsource"); > - return FALSE; > - } > - > - if (rdma->wr_data[0].control_len) { > - cond |= G_IO_IN; > - } > - cond |= G_IO_OUT; > > - return (*func)(QIO_CHANNEL(rsource->rioc), > - (cond & rsource->condition), > - user_data); > + return (*func)(QIO_CHANNEL(rsource->rioc), rsource->condition, user_data); No idea who even calls g_source_set_callback() in this case. What is func? > } > > static void