From: Willem de Bruijn <willemb@xxxxxxxxxx> Add napi for virtio-net transmit completion processing. Based on previous patchsets by Jason Wang: [RFC V7 PATCH 0/7] enable tx interrupts for virtio-net http://lkml.iu.edu/hypermail/linux/kernel/1505.3/00245.html Changes: RFC -> v1: - dropped vhost interrupt moderation patch: not needed and likely expensive at light load - remove tx napi weight - always clean all tx completions - use boolean to toggle tx-napi, instead - only clean tx in rx if tx-napi is enabled - then clean tx before rx - fix: add missing braces in virtnet_freeze_down - testing: add 4KB TCP_RR + UDP test results Before commit b0c39dbdc204 ("virtio_net: don't free buffers in xmit ring") the virtio-net driver would free transmitted packets on transmission of new packets in ndo_start_xmit and, to catch the edge case when no new packet is sent, also in a timer at 10HZ. A timer can cause long stalls. VIRTIO_F_NOTIFY_ON_EMPTY avoids stalls due to low free descriptor count. It does not address a stalls due to low socket SO_SNDBUF. Increasing timer frequency decreases that stall time, but increases interrupt rate and, thus, cycle count. Currently, with no timer, packets are freed only at ndo_start_xmit. Latency of consume_skb is now unbounded. To avoid a deadlock if a sock reaches SO_SNDBUF, packets are orphaned on tx. This breaks TCP small queues. Reenable TCP small queues by removing the orphan. Instead of using a timer, convert the driver to regular tx napi. This does not have the unresolved stall issue and does not have any frequency to tune. By keeping interrupts enabled by default, napi increases tx interrupt rate. VIRTIO_F_EVENT_IDX avoids sending an interrupt if one is already unacknowledged, so makes this more feasible today. Combine that with an optimization that brings interrupt rate back in line with the existing version for most workloads: Tx completion cleaning on rx interrupts elides most explicit tx interrupts by relying on the fact that many rx interrupts fire. Tested by running {1, 10, 100} {TCP, UDP} STREAM, RR, 4K_RR benchmarks from a guest to a server on the host, on an x86_64 Haswell. The guest runs 4 vCPUs pinned to 4 cores. vhost and the test server are pinned to a core each. All results are the median of 5 runs, with variance well < 10%. Used neper (github.com/google/neper) as test process. Napi increases single stream throughput, but increases cycle cost. Processing completions on rx interrupts optimization brings this down, especially for bi-directional workloads. UDP_STREAM is unidirectional and continues to see a ~10% lower throughput. Not showing number for only the optimization patch. That showed no significant difference with upstream. upstream napi +at-rx TCP_STREAM: 1x: Mbps 30537 37666 37910 Gcycles 400 540 405 10x: Mbps 41012 39954 40245 Gcycles 434 546 421 100x: Mbps 34088 34172 34245 Gcycles 435 546 418 TCP_RR Latency (us): 1x: p50 24 24 21 p99 27 27 27 Gcycles 299 432 308 10x: p50 31 31 41 p99 40 46 52 Gcycles 346 428 322 100x: p50 155 151 310 p99 334 329 362 Gcycles 336 421 308 TCP_RR 4K: 1x: p50 30 30 27 p99 34 33 34 Gcycles 307 437 305 10x: p50 63 67 65 p99 76 77 87 Gcycles 334 425 315 100x: p50 421 497 511 p99 510 571 773 Gcycles 350 430 321 UDP_STREAM: 1x: Mbps 29802 26360 26608 Gcycles 305 363 362 10x: Mbps 29901 26801 27078 Gcycles 287 363 360 100x: Mbps 29952 26822 27054 Gcycles 336 351 354 UDP_RR: 1x: p50 24 21 19 p99 27 24 23 Gcycles 299 431 309 10x: p50 31 27 35 p99 40 35 54 Gcycles 346 421 325 100x: p50 155 153 240 p99 334 323 462 Gcycles 336 421 311 UDP_RR 4K: 1x: p50 24 25 23 p99 27 28 30 Gcycles 299 435 321 10x: p50 31 35 48 p99 40 54 66 Gcycles 346 451 308 100x: p50 155 210 307 p99 334 451 519 Gcycles 336 440 297 Note that GSO is enabled, so 4K RR still translates to one packet per request. Lower throughput at 100x vs 10x can be (at least in part) explained by looking at bytes per packet sent (nstat). It likely also explains the lower throughput of 1x for some variants. upstream: N=1 bytes/pkt=16581 N=10 bytes/pkt=61513 N=100 bytes/pkt=51558 at_rx: N=1 bytes/pkt=65204 N=10 bytes/pkt=65148 N=100 bytes/pkt=56840 Willem de Bruijn (3): virtio-net: napi helper functions virtio-net: transmit napi virtio-net: clean tx descriptors from rx napi drivers/net/virtio_net.c | 150 ++++++++++++++++++++++++++++++++++------------- 1 file changed, 110 insertions(+), 40 deletions(-) -- 2.12.2.564.g063fe858b8-goog _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
