On Mon, Jul 15, 2024 at 01:09:59PM +0000, Liu, Yuan1 wrote: > > -----Original Message----- > > From: Michael S. Tsirkin <m...@redhat.com> > > Sent: Monday, July 15, 2024 8:24 PM > > To: Liu, Yuan1 <yuan1....@intel.com> > > Cc: Wang, Yichen <yichen.w...@bytedance.com>; Paolo Bonzini > > <pbonz...@redhat.com>; Marc-André Lureau <marcandre.lur...@redhat.com>; > > Daniel P. Berrangé <berra...@redhat.com>; Thomas Huth <th...@redhat.com>; > > Philippe Mathieu-Daudé <phi...@linaro.org>; Peter Xu <pet...@redhat.com>; > > Fabiano Rosas <faro...@suse.de>; Eric Blake <ebl...@redhat.com>; Markus > > Armbruster <arm...@redhat.com>; Cornelia Huck <coh...@redhat.com>; qemu- > > de...@nongnu.org; Hao Xiang <hao.xi...@linux.dev>; Kumar, Shivam > > <shivam.kum...@nutanix.com>; Ho-Ren (Jack) Chuang > > <horenchu...@bytedance.com> > > 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 <m...@redhat.com> > > > > Sent: Friday, July 12, 2024 6:49 AM > > > > To: Wang, Yichen <yichen.w...@bytedance.com> > > > > Cc: Paolo Bonzini <pbonz...@redhat.com>; Marc-André Lureau > > > > <marcandre.lur...@redhat.com>; Daniel P. Berrangé > > <berra...@redhat.com>; > > > > Thomas Huth <th...@redhat.com>; Philippe Mathieu-Daudé > > > > <phi...@linaro.org>; Peter Xu <pet...@redhat.com>; Fabiano Rosas > > > > <faro...@suse.de>; Eric Blake <ebl...@redhat.com>; Markus Armbruster > > > > <arm...@redhat.com>; Cornelia Huck <coh...@redhat.com>; qemu- > > > > de...@nongnu.org; Hao Xiang <hao.xi...@linux.dev>; Liu, Yuan1 > > > > <yuan1....@intel.com>; Kumar, Shivam <shivam.kum...@nutanix.com>; Ho- > > Ren > > > > (Jack) Chuang <horenchu...@bytedance.com> > > > > 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
