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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id j3-20020adfea43000000b0020d02262664sm21585668wrn.25.2022.06.08.10.59.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Jun 2022 10:59:33 -0700 (PDT) Date: Wed, 8 Jun 2022 18:59:30 +0100 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Stefan Hajnoczi , Hailiang Zhang , Juan Quintela , Fam Zheng Subject: Re: [PATCH 03/20] migration: remove unreachble RDMA code in save_hook impl Message-ID: References: <20220524110235.145079-1-berrange@redhat.com> <20220524110235.145079-4-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220524110235.145079-4-berrange@redhat.com> User-Agent: Mutt/2.2.1 (2022-02-19) Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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" * Daniel P. Berrangé (berrange@redhat.com) wrote: > The QEMUFile 'save_hook' callback has a 'size_t size' parameter. > > The RDMA impl of this has logic that takes different actions > depending on whether the value is zero or non-zero. It has > commented out logic that would have taken further actions > if the value was negative. > > The only place where the 'save_hook' callback is invoked is > the ram_control_save_page() method, which passes 'size' > through from its caller. The only caller of this method is > in turn control_save_page(). This method unconditionally > passes the 'TARGET_PAGE_SIZE' constant for the 'size' parameter. > > IOW, the only scenario for 'size' that can execute in the > qemu_rdma_save_page method is 'size > 0'. The remaining code > has been unreachable since RDMA support was first introduced > 9 years ago. > > Signed-off-by: Daniel P. Berrangé Ah good; less rdma code! Reviewed-by: Dr. David Alan Gilbert > --- > migration/rdma.c | 120 +++++++++-------------------------------------- > 1 file changed, 21 insertions(+), 99 deletions(-) > > diff --git a/migration/rdma.c b/migration/rdma.c > index 672d1958a9..6e7756bee7 100644 > --- a/migration/rdma.c > +++ b/migration/rdma.c > @@ -1486,34 +1486,6 @@ static uint64_t qemu_rdma_make_wrid(uint64_t wr_id, uint64_t index, > return result; > } > > -/* > - * Set bit for unregistration in the next iteration. > - * We cannot transmit right here, but will unpin later. > - */ > -static void qemu_rdma_signal_unregister(RDMAContext *rdma, uint64_t index, > - uint64_t chunk, uint64_t wr_id) > -{ > - if (rdma->unregistrations[rdma->unregister_next] != 0) { > - error_report("rdma migration: queue is full"); > - } else { > - RDMALocalBlock *block = &(rdma->local_ram_blocks.block[index]); > - > - if (!test_and_set_bit(chunk, block->unregister_bitmap)) { > - trace_qemu_rdma_signal_unregister_append(chunk, > - rdma->unregister_next); > - > - rdma->unregistrations[rdma->unregister_next++] = > - qemu_rdma_make_wrid(wr_id, index, chunk); > - > - if (rdma->unregister_next == RDMA_SIGNALED_SEND_MAX) { > - rdma->unregister_next = 0; > - } > - } else { > - trace_qemu_rdma_signal_unregister_already(chunk); > - } > - } > -} > - > /* > * Consult the connection manager to see a work request > * (of any kind) has completed. > @@ -3278,23 +3250,7 @@ qio_channel_rdma_shutdown(QIOChannel *ioc, > * Offset is an offset to be added to block_offset and used > * to also lookup the corresponding RAMBlock. > * > - * @size > 0 : > - * Initiate an transfer this size. > - * > - * @size == 0 : > - * A 'hint' or 'advice' that means that we wish to speculatively > - * and asynchronously unregister this memory. In this case, there is no > - * guarantee that the unregister will actually happen, for example, > - * if the memory is being actively transmitted. Additionally, the memory > - * may be re-registered at any future time if a write within the same > - * chunk was requested again, even if you attempted to unregister it > - * here. > - * > - * @size < 0 : TODO, not yet supported > - * Unregister the memory NOW. This means that the caller does not > - * expect there to be any future RDMA transfers and we just want to clean > - * things up. This is used in case the upper layer owns the memory and > - * cannot wait for qemu_fclose() to occur. > + * @size : Number of bytes to transfer > * > * @bytes_sent : User-specificed pointer to indicate how many bytes were > * sent. Usually, this will not be more than a few bytes of > @@ -3323,61 +3279,27 @@ static size_t qemu_rdma_save_page(QEMUFile *f, void *opaque, > > qemu_fflush(f); > > - if (size > 0) { > - /* > - * Add this page to the current 'chunk'. If the chunk > - * is full, or the page doesn't belong to the current chunk, > - * an actual RDMA write will occur and a new chunk will be formed. > - */ > - ret = qemu_rdma_write(f, rdma, block_offset, offset, size); > - if (ret < 0) { > - error_report("rdma migration: write error! %d", ret); > - goto err; > - } > - > - /* > - * We always return 1 bytes because the RDMA > - * protocol is completely asynchronous. We do not yet know > - * whether an identified chunk is zero or not because we're > - * waiting for other pages to potentially be merged with > - * the current chunk. So, we have to call qemu_update_position() > - * later on when the actual write occurs. > - */ > - if (bytes_sent) { > - *bytes_sent = 1; > - } > - } else { > - uint64_t index, chunk; > - > - /* TODO: Change QEMUFileOps prototype to be signed: size_t => long > - if (size < 0) { > - ret = qemu_rdma_drain_cq(f, rdma); > - if (ret < 0) { > - fprintf(stderr, "rdma: failed to synchronously drain" > - " completion queue before unregistration.\n"); > - goto err; > - } > - } > - */ > - > - ret = qemu_rdma_search_ram_block(rdma, block_offset, > - offset, size, &index, &chunk); > - > - if (ret) { > - error_report("ram block search failed"); > - goto err; > - } > - > - qemu_rdma_signal_unregister(rdma, index, chunk, 0); > + /* > + * Add this page to the current 'chunk'. If the chunk > + * is full, or the page doesn't belong to the current chunk, > + * an actual RDMA write will occur and a new chunk will be formed. > + */ > + ret = qemu_rdma_write(f, rdma, block_offset, offset, size); > + if (ret < 0) { > + error_report("rdma migration: write error! %d", ret); > + goto err; > + } > > - /* > - * TODO: Synchronous, guaranteed unregistration (should not occur during > - * fast-path). Otherwise, unregisters will process on the next call to > - * qemu_rdma_drain_cq() > - if (size < 0) { > - qemu_rdma_unregister_waiting(rdma); > - } > - */ > + /* > + * We always return 1 bytes because the RDMA > + * protocol is completely asynchronous. We do not yet know > + * whether an identified chunk is zero or not because we're > + * waiting for other pages to potentially be merged with > + * the current chunk. So, we have to call qemu_update_position() > + * later on when the actual write occurs. > + */ > + if (bytes_sent) { > + *bytes_sent = 1; > } > > /* > -- > 2.36.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK