virtio-net: auto-tune mergeable rx buffer size for improved performance
Commit 2613af0e ("virtio_net: migrate mergeable rx buffers to page frag allocators") changed the mergeable receive buffer size from PAGE_SIZE to MTU-size, introducing a single-stream regression for benchmarks with large average packet size. There is no single optimal buffer size for all workloads. For workloads with packet size <= MTU bytes, MTU + virtio-net header-sized buffers are preferred as larger buffers reduce the TCP window due to SKB truesize. However, single-stream workloads with large average packet sizes have higher throughput if larger (e.g., PAGE_SIZE) buffers are used. This commit auto-tunes the mergeable receiver buffer packet size by choosing the packet buffer size based on an EWMA of the recent packet sizes for the receive queue. Packet buffer sizes range from MTU_SIZE + virtio-net header len to PAGE_SIZE. This improves throughput for large packet workloads, as any workload with average packet size >= PAGE_SIZE will use PAGE_SIZE buffers. These optimizations interact positively with recent commit ba275241 ("virtio-net: coalesce rx frags when possible during rx"), which coalesces adjacent RX SKB fragments in virtio_net. The coalescing optimizations benefit buffers of any size. Benchmarks taken from an average of 5 netperf 30-second TCP_STREAM runs between two QEMU VMs on a single physical machine. Each VM has two VCPUs with all offloads & vhost enabled. All VMs and vhost threads run in a single 4 CPU cgroup cpuset, using cgroups to ensure that other processes in the system will not be scheduled on the benchmark CPUs. Trunk includes SKB rx frag coalescing. net-next w/ virtio_net before 2613af0e (PAGE_SIZE bufs): 14642.85Gb/s net-next (MTU-size bufs): 13170.01Gb/s net-next + auto-tune: 14555.94Gb/s Jason Wang also reported a throughput increase on mlx4 from 22Gb/s using MTU-sized buffers to about 26Gb/s using auto-tuning. Signed-off-by:Michael Dalton <mwdalton@google.com> Signed-off-by:
Please register or sign in to comment