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Tsirkin" To: "Liu, Yuan1" Cc: "Wang, Yichen" , Paolo Bonzini , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Thomas Huth , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Peter Xu , Fabiano Rosas , Eric Blake , Markus Armbruster , Cornelia Huck , "qemu-devel@nongnu.org" , Hao Xiang , "Kumar, Shivam" , "Ho-Ren (Jack) Chuang" Subject: Re: [PATCH v5 00/13] WIP: Use Intel DSA accelerator to offload zero page checking in multifd live migration. Message-ID: <20240715104015-mutt-send-email-mst@kernel.org> References: <20240711215244.19237-1-yichen.wang@bytedance.com> <20240711184131-mutt-send-email-mst@kernel.org> <20240715081857-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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 On Mon, Jul 15, 2024 at 01:09:59PM +0000, Liu, Yuan1 wrote: > > -----Original Message----- > > From: Michael S. Tsirkin > > Sent: Monday, July 15, 2024 8:24 PM > > To: Liu, Yuan1 > > Cc: Wang, Yichen ; Paolo Bonzini > > ; Marc-André Lureau ; > > Daniel P. Berrangé ; Thomas Huth ; > > Philippe Mathieu-Daudé ; Peter Xu ; > > Fabiano Rosas ; Eric Blake ; Markus > > Armbruster ; Cornelia Huck ; qemu- > > devel@nongnu.org; Hao Xiang ; Kumar, Shivam > > ; Ho-Ren (Jack) Chuang > > > > Subject: Re: [PATCH v5 00/13] WIP: Use Intel DSA accelerator to offload > > zero page checking in multifd live migration. > > > > On Mon, Jul 15, 2024 at 08:29:03AM +0000, Liu, Yuan1 wrote: > > > > -----Original Message----- > > > > From: Michael S. Tsirkin > > > > Sent: Friday, July 12, 2024 6:49 AM > > > > To: Wang, Yichen > > > > Cc: Paolo Bonzini ; Marc-André Lureau > > > > ; Daniel P. Berrangé > > ; > > > > Thomas Huth ; Philippe Mathieu-Daudé > > > > ; Peter Xu ; Fabiano Rosas > > > > ; Eric Blake ; Markus Armbruster > > > > ; Cornelia Huck ; qemu- > > > > devel@nongnu.org; Hao Xiang ; Liu, Yuan1 > > > > ; Kumar, Shivam ; Ho- > > Ren > > > > (Jack) Chuang > > > > Subject: Re: [PATCH v5 00/13] WIP: Use Intel DSA accelerator to > > offload > > > > zero page checking in multifd live migration. > > > > > > > > On Thu, Jul 11, 2024 at 02:52:35PM -0700, Yichen Wang wrote: > > > > > * Performance: > > > > > > > > > > We use two Intel 4th generation Xeon servers for testing. > > > > > > > > > > Architecture: x86_64 > > > > > CPU(s): 192 > > > > > Thread(s) per core: 2 > > > > > Core(s) per socket: 48 > > > > > Socket(s): 2 > > > > > NUMA node(s): 2 > > > > > Vendor ID: GenuineIntel > > > > > CPU family: 6 > > > > > Model: 143 > > > > > Model name: Intel(R) Xeon(R) Platinum 8457C > > > > > Stepping: 8 > > > > > CPU MHz: 2538.624 > > > > > CPU max MHz: 3800.0000 > > > > > CPU min MHz: 800.0000 > > > > > > > > > > We perform multifd live migration with below setup: > > > > > 1. VM has 100GB memory. > > > > > 2. Use the new migration option multifd-set-normal-page-ratio to > > control > > > > the total > > > > > size of the payload sent over the network. > > > > > 3. Use 8 multifd channels. > > > > > 4. Use tcp for live migration. > > > > > 4. Use CPU to perform zero page checking as the baseline. > > > > > 5. Use one DSA device to offload zero page checking to compare with > > the > > > > baseline. > > > > > 6. Use "perf sched record" and "perf sched timehist" to analyze CPU > > > > usage. > > > > > > > > > > A) Scenario 1: 50% (50GB) normal pages on an 100GB vm. > > > > > > > > > > CPU usage > > > > > > > > > > |---------------|---------------|---------------|------------- > > --| > > > > > | |comm |runtime(msec) |totaltime(msec)| > > > > > |---------------|---------------|---------------|------------- > > --| > > > > > |Baseline |live_migration |5657.58 | | > > > > > | |multifdsend_0 |3931.563 | | > > > > > | |multifdsend_1 |4405.273 | | > > > > > | |multifdsend_2 |3941.968 | | > > > > > | |multifdsend_3 |5032.975 | | > > > > > | |multifdsend_4 |4533.865 | | > > > > > | |multifdsend_5 |4530.461 | | > > > > > | |multifdsend_6 |5171.916 | | > > > > > | |multifdsend_7 |4722.769 |41922 | > > > > > |---------------|---------------|---------------|------------- > > --| > > > > > |DSA |live_migration |6129.168 | | > > > > > | |multifdsend_0 |2954.717 | | > > > > > | |multifdsend_1 |2766.359 | | > > > > > | |multifdsend_2 |2853.519 | | > > > > > | |multifdsend_3 |2740.717 | | > > > > > | |multifdsend_4 |2824.169 | | > > > > > | |multifdsend_5 |2966.908 | | > > > > > | |multifdsend_6 |2611.137 | | > > > > > | |multifdsend_7 |3114.732 | | > > > > > | |dsa_completion |3612.564 |32568 | > > > > > |---------------|---------------|---------------|------------- > > --| > > > > > > > > > > Baseline total runtime is calculated by adding up all multifdsend_X > > > > > and live_migration threads runtime. DSA offloading total runtime is > > > > > calculated by adding up all multifdsend_X, live_migration and > > > > > dsa_completion threads runtime. 41922 msec VS 32568 msec runtime and > > > > > that is 23% total CPU usage savings. > > > > > > > > > > > > Here the DSA was mostly idle. > > > > > > > > Sounds good but a question: what if several qemu instances are > > > > migrated in parallel? > > > > > > > > Some accelerators tend to basically stall if several tasks > > > > are trying to use them at the same time. > > > > > > > > Where is the boundary here? > > > > > > A DSA device can be assigned to multiple Qemu instances. > > > The DSA resource used by each process is called a work queue, each DSA > > > device can support up to 8 work queues and work queues are classified > > into > > > dedicated queues and shared queues. > > > > > > A dedicated queue can only serve one process. Theoretically, there is no > > limit > > > on the number of processes in a shared queue, it is based on enqcmd + > > SVM technology. > > > > > > https://www.kernel.org/doc/html/v5.17/x86/sva.html > > > > This server has 200 CPUs which can thinkably migrate around 100 single > > cpu qemu instances with no issue. What happens if you do this with DSA? > > First, the DSA work queue needs to be configured in shared mode, and one > queue is enough. > > The maximum depth of the work queue of the DSA hardware is 128, which means > that the number of zero-page detection tasks submitted cannot exceed 128, > otherwise, enqcmd will return an error until the work queue is available again > > 100 Qemu instances need to be migrated concurrently, I don't have any data on > this yet, I think the 100 zero-page detection tasks can be successfully submitted > to the DSA hardware work queue, but the throughput of DSA's zero-page detection also > needs to be considered. Once the DSA maximum throughput is reached, the work queue > may be filled up quickly, this will cause some Qemu instances to be temporarily unable > to submit new tasks to DSA. The unfortunate reality here would be that there's likely no QoS, this is purely fifo, right? > This is likely to happen in the first round of migration > memory iteration. Try testing this and see then? -- MST