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Tue, 14 Apr 2026 15:34:21 -0700 (PDT) X-Received: by 2002:a0c:e014:0:b0:89c:6692:1d83 with SMTP id 6a1803df08f44-8ac860e5ed8mr258224416d6.3.1776206060515; Tue, 14 Apr 2026 15:34:20 -0700 (PDT) Received: from x1.local ([142.189.10.167]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8acb508807fsm58307466d6.48.2026.04.14.15.34.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Apr 2026 15:34:19 -0700 (PDT) Date: Tue, 14 Apr 2026 18:34:17 -0400 From: Peter Xu To: Samuel Zhang Cc: qemu-devel@nongnu.org, farosas@suse.de, lizhijian@fujitsu.com, eblake@redhat.com, armbru@redhat.com, Emily.Deng@amd.com, Victor.Zhao@amd.com, PengJu.Zhou@amd.com, Qing.Ma@amd.com Subject: Re: [PATCH v5] migration/rdma: add x-rdma-chunk-size parameter Message-ID: References: <20260413035703.2602065-1-guoqing.zhang@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260413035703.2602065-1-guoqing.zhang@amd.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: qemu development 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 Mon, Apr 13, 2026 at 11:57:03AM +0800, Samuel Zhang wrote: > The default 1MB RDMA chunk size causes slow live migration because > each chunk triggers a write_flush (ibv_post_send). For 8GB RAM, > 1MB chunk size produces ~15000 flushes vs ~3700 with 1024MB chunk size. > > Add x-rdma-chunk-size parameter to configure the RDMA chunk size for > faster migration. > Usage: `migrate_set_parameter x-rdma-chunk-size 1024M` > > Performance with RDMA live migration of 8GB RAM VM: > > | x-rdma-chunk-size (B) | time (s) | throughput (MB/s) | > |-----------------------|----------|-------------------| > | 1M (default) | 37.915 | 1,007 | > | 32M | 17.880 | 2,260 | > | 1024M | 4.368 | 17,529 | > > Signed-off-by: Samuel Zhang > Acked-by: Markus Armbruster > Acked-by: Li Zhijian > Tested-by: Li Zhijian Acked-by: Peter Xu -- Peter Xu