Hello Hao, On Mon, Nov 13, 2023 at 9:42 PM Hao Xiang <hao.xi...@bytedance.com> wrote: > > v2 > * Rebase on top of 3e01f1147a16ca566694b97eafc941d62fa1e8d8. > * Leave Juan's changes in their original form instead of squashing them. > * Add a new commit to refactor the multifd_send_thread function to prepare > for introducing the DSA offload functionality. > * Use page count to configure multifd-packet-size option. > * Don't use the FLAKY flag in DSA tests. > * Test if DSA integration test is setup correctly and skip the test if > * not. > * Fixed broken link in the previous patch cover. > > * Background: > > I posted an RFC about DSA offloading in QEMU: > https://patchew.org/QEMU/20230529182001.2232069-1-hao.xi...@bytedance.com/ > > This patchset implements the DSA offloading on zero page checking in > multifd live migration code path. >
Do you have performance numbers with different packet sizes for DSA and non-DSA cases? What have you found was an optimal size for DSA offloading? Thank you! > * Overview: > > Intel Data Streaming Accelerator(DSA) is introduced in Intel's 4th generation > Xeon server, aka Sapphire Rapids. > https://cdrdv2-public.intel.com/671116/341204-intel-data-streaming-accelerator-spec.pdf > https://www.intel.com/content/www/us/en/content-details/759709/intel-data-streaming-accelerator-user-guide.html > One of the things DSA can do is to offload memory comparison workload from > CPU to DSA accelerator hardware. This patchset implements a solution to > offload > QEMU's zero page checking from CPU to DSA accelerator hardware. We gain > two benefits from this change: > 1. Reduces CPU usage in multifd live migration workflow across all use > cases. > 2. Reduces migration total time in some use cases. > > * Design: > > These are the logical steps to perform DSA offloading: > 1. Configure DSA accelerators and create user space openable DSA work > queues via the idxd driver. > 2. Map DSA's work queue into a user space address space. > 3. Fill an in-memory task descriptor to describe the memory operation. > 4. Use dedicated CPU instruction _enqcmd to queue a task descriptor to > the work queue. > 5. Pull the task descriptor's completion status field until the task > completes. > 6. Check return status. > > The memory operation is now totally done by the accelerator hardware but > the new workflow introduces overheads. The overhead is the extra cost CPU > prepares and submits the task descriptors and the extra cost CPU pulls for > completion. The design is around minimizing these two overheads. > > 1. In order to reduce the overhead on task preparation and submission, > we use batch descriptors. A batch descriptor will contain N individual > zero page checking tasks where the default N is 128 (default packet size > / page size) and we can increase N by setting the packet size via a new > migration option. > 2. The multifd sender threads prepares and submits batch tasks to DSA > hardware and it waits on a synchronization object for task completion. > Whenever a DSA task is submitted, the task structure is added to a > thread safe queue. It's safe to have multiple multifd sender threads to > submit tasks concurrently. > 3. Multiple DSA hardware devices can be used. During multifd initialization, > every sender thread will be assigned a DSA device to work with. We > use a round-robin scheme to evenly distribute the work across all used > DSA devices. > 4. Use a dedicated thread dsa_completion to perform busy pulling for all > DSA task completions. The thread keeps dequeuing DSA tasks from the > thread safe queue. The thread blocks when there is no outstanding DSA > task. When pulling for completion of a DSA task, the thread uses CPU > instruction _mm_pause between the iterations of a busy loop to save some > CPU power as well as optimizing core resources for the other hypercore. > 5. DSA accelerator can encounter errors. The most popular error is a > page fault. We have tested using devices to handle page faults but > performance is bad. Right now, if DSA hits a page fault, we fallback to > use CPU to complete the rest of the work. The CPU fallback is done in > the multifd sender thread. > 6. Added a new migration option multifd-dsa-accel to set the DSA device > path. If set, the multifd workflow will leverage the DSA devices for > offloading. > 7. Added a new migration option multifd-normal-page-ratio to make > multifd live migration easier to test. Setting a normal page ratio will > make live migration recognize a zero page as a normal page and send > the entire payload over the network. If we want to send a large network > payload and analyze throughput, this option is useful. > 8. Added a new migration option multifd-packet-size. This can increase > the number of pages being zero page checked and sent over the network. > The extra synchronization between the sender threads and the dsa > completion thread is an overhead. Using a large packet size can reduce > that overhead. > > * 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. > > Latency > > |---------------|---------------|---------------|---------------|---------------|---------------| > | |total time |down time |throughput > |transferred-ram|total-ram | > > |---------------|---------------|---------------|---------------|---------------|---------------| > |Baseline |10343 ms |161 ms |41007.00 mbps > |51583797 kb |102400520 kb | > > |---------------|---------------|---------------|---------------|-------------------------------| > |DSA offload |9535 ms |135 ms |46554.40 mbps > |53947545 kb |102400520 kb | > > |---------------|---------------|---------------|---------------|---------------|---------------| > > Total time is 8% faster and down time is 16% faster. > > B) Scenario 2: 100% (100GB) zero pages on an 100GB vm. > > CPU usage > |---------------|---------------|---------------|---------------| > | |comm |runtime(msec) |totaltime(msec)| > |---------------|---------------|---------------|---------------| > |Baseline |live_migration |4860.718 | | > | |multifdsend_0 |748.875 | | > | |multifdsend_1 |898.498 | | > | |multifdsend_2 |787.456 | | > | |multifdsend_3 |764.537 | | > | |multifdsend_4 |785.687 | | > | |multifdsend_5 |756.941 | | > | |multifdsend_6 |774.084 | | > | |multifdsend_7 |782.900 |11154 | > |---------------|---------------|-------------------------------| > |DSA offloading |live_migration |3846.976 | | > | |multifdsend_0 |191.880 | | > | |multifdsend_1 |166.331 | | > | |multifdsend_2 |168.528 | | > | |multifdsend_3 |197.831 | | > | |multifdsend_4 |169.580 | | > | |multifdsend_5 |167.984 | | > | |multifdsend_6 |198.042 | | > | |multifdsend_7 |170.624 | | > | |dsa_completion |3428.669 |8700 | > |---------------|---------------|---------------|---------------| > > Baseline total runtime is 11154 msec and DSA offloading total runtime is > 8700 msec. That is 22% CPU savings. > > Latency > > |--------------------------------------------------------------------------------------------| > | |total time |down time |throughput > |transferred-ram|total-ram | > > |---------------|---------------|---------------|---------------|---------------|------------| > |Baseline |4867 ms |20 ms |1.51 mbps |565 > kb |102400520 kb| > > |---------------|---------------|---------------|---------------|----------------------------| > |DSA offload |3888 ms |18 ms |1.89 mbps |565 > kb |102400520 kb| > > |---------------|---------------|---------------|---------------|---------------|------------| > > Total time 20% faster and down time 10% faster. > > * Testing: > > 1. Added unit tests for cover the added code path in dsa.c > 2. Added integration tests to cover multifd live migration using DSA > offloading. > > * Patchset > > Apply this patchset on top of commit > f78ea7ddb0e18766ece9fdfe02061744a7afc41b > > Hao Xiang (16): > meson: Introduce new instruction set enqcmd to the build system. > util/dsa: Add dependency idxd. > util/dsa: Implement DSA device start and stop logic. > util/dsa: Implement DSA task enqueue and dequeue. > util/dsa: Implement DSA task asynchronous completion thread model. > util/dsa: Implement zero page checking in DSA task. > util/dsa: Implement DSA task asynchronous submission and wait for > completion. > migration/multifd: Add new migration option for multifd DSA > offloading. > migration/multifd: Prepare to introduce DSA acceleration on the > multifd path. > migration/multifd: Enable DSA offloading in multifd sender path. > migration/multifd: Add test hook to set normal page ratio. > migration/multifd: Enable set normal page ratio test hook in multifd. > migration/multifd: Add migration option set packet size. > migration/multifd: Enable set packet size migration option. > util/dsa: Add unit test coverage for Intel DSA task submission and > completion. > migration/multifd: Add integration tests for multifd with Intel DSA > offloading. > > Juan Quintela (4): > multifd: Add capability to enable/disable zero_page > multifd: Support for zero pages transmission > multifd: Zero pages transmission > So we use multifd to transmit zero pages. > > include/qemu/dsa.h | 119 ++++ > linux-headers/linux/idxd.h | 356 ++++++++++ > meson.build | 2 + > meson_options.txt | 2 + > migration/migration-hmp-cmds.c | 22 + > migration/multifd-zlib.c | 8 +- > migration/multifd-zstd.c | 8 +- > migration/multifd.c | 203 +++++- > migration/multifd.h | 28 +- > migration/options.c | 107 +++ > migration/options.h | 4 + > migration/ram.c | 45 +- > migration/trace-events | 8 +- > qapi/migration.json | 53 +- > scripts/meson-buildoptions.sh | 3 + > tests/qtest/migration-test.c | 77 ++- > tests/unit/meson.build | 6 + > tests/unit/test-dsa.c | 466 +++++++++++++ > util/dsa.c | 1132 ++++++++++++++++++++++++++++++++ > util/meson.build | 1 + > 20 files changed, 2612 insertions(+), 38 deletions(-) > create mode 100644 include/qemu/dsa.h > create mode 100644 linux-headers/linux/idxd.h > create mode 100644 tests/unit/test-dsa.c > create mode 100644 util/dsa.c > > -- > 2.30.2 > > -- Elena
