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Thu, 01 Feb 2024 16:28:57 -0800 (PST) X-Forwarded-Encrypted: i=0; AJvYcCUfxGBFNH4GVEiVx5dOIlT8G0kt5Hfq8SIxBZULw3zXMiTAtyJV9Ef7O7rtjaweSUaqBQJ1U0kxmQEU6kzp0CG3zaXv8uG1O6IVFlPN745FuKFHEyQ9Xser9Zs7MolxqcljM4VV7kSaTFVCVUlijjBX5ShCoZIsFhxhDjf4NjzTwpO3BTuFv7uwiOEh+TiaZDGTHamMRhvB4N+Wnmzc2ug= Received: from x1n ([43.228.180.230]) by smtp.gmail.com with ESMTPSA id c26-20020aa7881a000000b006d9be753ac7sm340814pfo.108.2024.02.01.16.28.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Feb 2024 16:28:57 -0800 (PST) Date: Fri, 2 Feb 2024 08:28:47 +0800 From: Peter Xu To: Fabiano Rosas Cc: qemu-devel@nongnu.org, Bryan Zhang , Prasad Pandit , Yuan Liu , Avihai Horon , Hao Xiang Subject: Re: [PATCH 04/14] migration/multifd: Postpone reset of MultiFDPages_t Message-ID: References: <20240131103111.306523-1-peterx@redhat.com> <20240131103111.306523-5-peterx@redhat.com> <87wmrpjzew.fsf@suse.de> <87plxgi51k.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87plxgi51k.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: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.292, 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_H5=0.001, RCVD_IN_MSPIKE_WL=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 Thu, Feb 01, 2024 at 12:21:27PM -0300, Fabiano Rosas wrote: > Peter Xu writes: > > > On Wed, Jan 31, 2024 at 12:27:51PM -0300, Fabiano Rosas wrote: > >> > +/* Reset a MultiFDPages_t* object for the next use */ > >> > +static void multifd_pages_reset(MultiFDPages_t *pages) > >> > +{ > >> > + /* > >> > + * We don't need to touch offset[] array, because it will be > >> > + * overwritten later when reused. > >> > + */ > >> > + pages->num = 0; > >> > + pages->block = NULL; > >> > >> Having to do this at all is a huge overloading of this field. This not > >> only resets it, but it also communicates to multifd_queue_page() that > >> the previous payload has been sent. Otherwise, multifd_queue_page() > >> wouldn't know whether the previous call to multifd_queue_page() has > >> called multifd_send_pages() or if it has exited early. So this basically > >> means "the block that was previously here has been sent". > >> > >> That's why we need the changed=true logic. A > >> multifd_send_state->pages->block still has a few pages left to send, but > >> because it's less than pages->allocated, it skips > >> multifd_send_pages(). The next call to multifd_queue_page() already has > >> the next ramblock. So we set changed=true, call multifd_send_pages() to > >> send the remaining pages of that block and recurse into > >> multifd_queue_page() once more to send the new block. > > > > I agree, the queue page routines are not easy to follow as well. > > > > How do you like a rewrite of the queue logic, like this? > > > > ===== > > bool multifd_queue_page(RAMBlock *block, ram_addr_t offset) > > { > > MultiFDPages_t *pages; > > > > retry: > > pages = multifd_send_state->pages; > > > > /* If the queue is empty, we can already enqueue now */ > > if (multifd_queue_empty(pages)) { > > pages->block = block; > > multifd_enqueue(pages, offset); > > return true; > > } > > > > /* > > * Not empty, meanwhile we need a flush. It can because of either: > > * > > * (1) The page is not on the same ramblock of previous ones, or, > > * (2) The queue is full. > > * > > * After flush, always retry. > > */ > > if (pages->block != block || multifd_queue_full(pages)) { > > if (!multifd_send_pages()) { > > return false; > > } > > goto retry; > > } > > > > /* Not empty, and we still have space, do it! */ > > multifd_enqueue(pages, offset); > > return true; > > } > > ===== > > > > Would this be clearer? With above, we can drop the ->ramblock reset, > > afaict. > > > > I attached three patches if you agree it's better, then I'll include them > > in v2. > > Yes, let's do it. > > > > > -- > > Peter Xu > > From c5dc2052794efd6da6a1e6f4b49f25d5b32879f7 Mon Sep 17 00:00:00 2001 > > From: Peter Xu > > Date: Thu, 1 Feb 2024 17:50:21 +0800 > > Subject: [PATCH 1/3] migration/multifd: Change retval of multifd_queue_page() > > > > Using int is an overkill when there're only two options. Change it to a > > boolean. > > > > Signed-off-by: Peter Xu > > --- > > migration/multifd.h | 2 +- > > migration/multifd.c | 9 +++++---- > > migration/ram.c | 2 +- > > 3 files changed, 7 insertions(+), 6 deletions(-) > > > > diff --git a/migration/multifd.h b/migration/multifd.h > > index 34a2ecb9f4..a320c53a6f 100644 > > --- a/migration/multifd.h > > +++ b/migration/multifd.h > > @@ -22,7 +22,7 @@ bool multifd_recv_all_channels_created(void); > > void multifd_recv_new_channel(QIOChannel *ioc, Error **errp); > > void multifd_recv_sync_main(void); > > int multifd_send_sync_main(void); > > -int multifd_queue_page(RAMBlock *block, ram_addr_t offset); > > +bool multifd_queue_page(RAMBlock *block, ram_addr_t offset); > > > > /* Multifd Compression flags */ > > #define MULTIFD_FLAG_SYNC (1 << 0) > > diff --git a/migration/multifd.c b/migration/multifd.c > > index 91be6d2fc4..d0a3b4e062 100644 > > --- a/migration/multifd.c > > +++ b/migration/multifd.c > > @@ -505,7 +505,8 @@ static int multifd_send_pages(void) > > return 1; > > } > > > > -int multifd_queue_page(RAMBlock *block, ram_addr_t offset) > > +/* Returns true if enqueue successful, false otherwise */ > > +bool multifd_queue_page(RAMBlock *block, ram_addr_t offset) > > { > > MultiFDPages_t *pages = multifd_send_state->pages; > > bool changed = false; > > @@ -519,21 +520,21 @@ int multifd_queue_page(RAMBlock *block, ram_addr_t offset) > > pages->num++; > > > > if (pages->num < pages->allocated) { > > - return 1; > > + return true; > > } > > } else { > > changed = true; > > } > > > > if (multifd_send_pages() < 0) { > > - return -1; > > + return false; > > } > > > > if (changed) { > > return multifd_queue_page(block, offset); > > } > > > > - return 1; > > + return true; > > } > > > > /* Multifd send side hit an error; remember it and prepare to quit */ > > diff --git a/migration/ram.c b/migration/ram.c > > index d5b7cd5ac2..4649a81204 100644 > > --- a/migration/ram.c > > +++ b/migration/ram.c > > @@ -1252,7 +1252,7 @@ static int ram_save_page(RAMState *rs, PageSearchStatus *pss) > > > > static int ram_save_multifd_page(RAMBlock *block, ram_addr_t offset) > > { > > - if (multifd_queue_page(block, offset) < 0) { > > + if (!multifd_queue_page(block, offset)) { > > return -1; > > } > > stat64_add(&mig_stats.normal_pages, 1); > > -- > > 2.43.0 > > > > From f393f1cfe95d79bed72e6043903ee4c4cb298c21 Mon Sep 17 00:00:00 2001 > > From: Peter Xu > > Date: Thu, 1 Feb 2024 17:51:38 +0800 > > Subject: [PATCH 2/3] migration/multifd: Change retval of multifd_send_pages() > > > > Using int is an overkill when there're only two options. Change it to a > > boolean. > > > > Signed-off-by: Peter Xu > > --- > > migration/multifd.c | 15 ++++++++------- > > 1 file changed, 8 insertions(+), 7 deletions(-) > > > > diff --git a/migration/multifd.c b/migration/multifd.c > > index d0a3b4e062..d2b0f0eda9 100644 > > --- a/migration/multifd.c > > +++ b/migration/multifd.c > > @@ -449,9 +449,10 @@ static void multifd_send_kick_main(MultiFDSendParams *p) > > * thread is using the channel mutex when changing it, and the channel > > * have to had finish with its own, otherwise pending_job can't be > > * false. > > + * > > + * Returns true if succeed, false otherwise. > > */ > > - > > -static int multifd_send_pages(void) > > +static bool multifd_send_pages(void) > > { > > int i; > > static int next_channel; > > @@ -459,7 +460,7 @@ static int multifd_send_pages(void) > > MultiFDPages_t *pages = multifd_send_state->pages; > > > > if (multifd_send_should_exit()) { > > - return -1; > > + return false; > > } > > > > /* We wait here, until at least one channel is ready */ > > @@ -473,7 +474,7 @@ static int multifd_send_pages(void) > > next_channel %= migrate_multifd_channels(); > > for (i = next_channel;; i = (i + 1) % migrate_multifd_channels()) { > > if (multifd_send_should_exit()) { > > - return -1; > > + return false; > > } > > p = &multifd_send_state->params[i]; > > /* > > @@ -502,7 +503,7 @@ static int multifd_send_pages(void) > > qemu_mutex_unlock(&p->mutex); > > qemu_sem_post(&p->sem); > > > > - return 1; > > + return true; > > } > > > > /* Returns true if enqueue successful, false otherwise */ > > @@ -526,7 +527,7 @@ bool multifd_queue_page(RAMBlock *block, ram_addr_t offset) > > changed = true; > > } > > > > - if (multifd_send_pages() < 0) { > > + if (!multifd_send_pages()) { > > return false; > > } > > > > @@ -666,7 +667,7 @@ int multifd_send_sync_main(void) > > return 0; > > } > > if (multifd_send_state->pages->num) { > > - if (multifd_send_pages() < 0) { > > + if (!multifd_send_pages()) { > > error_report("%s: multifd_send_pages fail", __func__); > > return -1; > > } > > -- > > 2.43.0 > > > > From fcddc942cb31bc9d395d67a555d9a2281da452b1 Mon Sep 17 00:00:00 2001 > > From: Peter Xu > > Date: Thu, 1 Feb 2024 17:55:42 +0800 > > Subject: [PATCH 3/3] migration/multifd: Rewrite multifd_queue_page() > > > > The current multifd_queue_page() is not easy to read and follow. It is not > > good with a few reasons: > > > > - No helper at all to show what exactly does a condition mean; in short, > > readability is low. > > > > - Rely on pages->ramblock being cleared to detect an empty queue. It's > > slightly an overload of the ramblock pointer, per Fabiano [1], which I > > also agree. > > > > - Contains a self recursion, even if not necessary.. > > > > Rewrite this function. We add some comments to make it even clearer on > > what it does. > > > > [1] https://lore.kernel.org/r/87wmrpjzew.fsf@suse.de > > > > Signed-off-by: Peter Xu > > --- > > migration/multifd.c | 56 ++++++++++++++++++++++++++++++--------------- > > 1 file changed, 37 insertions(+), 19 deletions(-) > > > > diff --git a/migration/multifd.c b/migration/multifd.c > > index d2b0f0eda9..5a64a9c2e2 100644 > > --- a/migration/multifd.c > > +++ b/migration/multifd.c > > @@ -506,35 +506,53 @@ static bool multifd_send_pages(void) > > return true; > > } > > > > +static inline bool multifd_queue_empty(MultiFDPages_t *pages) > > +{ > > + return pages->num == 0; > > +} > > Good, because we can later switch from pages to something else entirely. > > > + > > +static inline bool multifd_queue_full(MultiFDPages_t *pages) > > +{ > > + return pages->num == pages->allocated; > > +} > > Pages allocated is nonsense. See if you agree with its removal: > https://gitlab.com/farosas/qemu/-/commit/7cfff1a3e31b271e901a6c08d8b5d8c01b680e4d > > --- > From 7cfff1a3e31b271e901a6c08d8b5d8c01b680e4d Mon Sep 17 00:00:00 2001 > From: Fabiano Rosas > Date: Tue, 24 Oct 2023 19:03:41 -0300 > Subject: [PATCH] multifd: Remove MultiFDPage_t:allocated > > When dealing with RAM, having a field called 'allocated' is > confusing. This field simply holds number of pages that fit in a > multifd packet. > > Since it is a constant dependent on the size of the multifd packet, > remove it and instead use the page size and MULTIFD_PACKET_SIZE > directly. > > This is another step in the direction of having no mentions of 'page' > in the multifd send thread. > > Signed-off-by: Fabiano Rosas > --- > migration/multifd.c | 6 ++---- > migration/multifd.h | 2 -- > 2 files changed, 2 insertions(+), 6 deletions(-) > > diff --git a/migration/multifd.c b/migration/multifd.c > index bdefce27706..83fb2caab04 100644 > --- a/migration/multifd.c > +++ b/migration/multifd.c > @@ -241,7 +241,6 @@ static MultiFDPages_t *multifd_pages_init(uint32_t n) > { > MultiFDPages_t *pages = g_new0(MultiFDPages_t, 1); > > - pages->allocated = n; > pages->offset = g_new0(ram_addr_t, n); > pages->page_size = qemu_target_page_size(); > > @@ -251,7 +250,6 @@ static MultiFDPages_t *multifd_pages_init(uint32_t n) > static void multifd_pages_clear(MultiFDPages_t *pages) > { > pages->num = 0; > - pages->allocated = 0; > pages->block = NULL; > g_free(pages->offset); > pages->offset = NULL; > @@ -264,7 +262,7 @@ static void multifd_send_fill_packet(MultiFDSendParams *p) > int i; > > packet->flags = cpu_to_be32(p->flags); > - packet->pages_alloc = cpu_to_be32(p->pages->allocated); > + packet->pages_alloc = cpu_to_be32(MULTIFD_PACKET_SIZE / p->pages->page_size); > packet->normal_pages = cpu_to_be32(p->pages->num); > packet->next_packet_size = cpu_to_be32(p->next_packet_size); > packet->packet_num = cpu_to_be64(p->packet_num); > @@ -451,7 +449,7 @@ int multifd_queue_page(RAMBlock *block, ram_addr_t offset) > pages->offset[pages->num] = offset; > pages->num++; > > - if (pages->num < pages->allocated) { > + if (pages->num * pages->page_size < MULTIFD_PACKET_SIZE) { > return 1; > } > } else { > diff --git a/migration/multifd.h b/migration/multifd.h > index 655f8d5eeb4..d1342296d63 100644 > --- a/migration/multifd.h > +++ b/migration/multifd.h > @@ -56,8 +56,6 @@ typedef struct { > typedef struct { > /* number of used pages */ > uint32_t num; > - /* number of allocated pages */ > - uint32_t allocated; > /* guest page size */ > uint32_t page_size; > /* offset of each page */ > -- I agree. Even if we would like to add a parameter to setup the allcated size (I remember one of the accelerator series has it), it'll still be a global variable rather than per-pages thing. I can cherry pick this and post together; will need a rebase but I can do that. -- Peter Xu