On Fri, 2010-09-17 at 15:33 +0530, Krishna Kumar wrote: > Following patches implement transmit MQ in virtio-net. Also > included is the user qemu changes. MQ is disabled by default > unless qemu specifies it. > > 1. This feature was first implemented with a single vhost. > Testing showed 3-8% performance gain for upto 8 netperf > sessions (and sometimes 16), but BW dropped with more > sessions. However, adding more vhosts improved BW > significantly all the way to 128 sessions. Multiple > vhost is implemented in-kernel by passing an argument > to SET_OWNER (retaining backward compatibility). The > vhost patch adds 173 source lines (incl comments). > 2. BW -> CPU/SD equation: Average TCP performance increased > 23% compared to almost 70% for earlier patch (with > unrestricted #vhosts). SD improved -4.2% while it had > increased 55% for the earlier patch. Increasing #vhosts > has it's pros and cons, but this patch lays emphasis on > reducing CPU utilization. Another option could be a > tunable to select number of vhosts threads. > 3. Interoperability: Many combinations, but not all, of qemu, > host, guest tested together. Tested with multiple i/f's > on guest, with both mq=on/off, vhost=on/off, etc. > > Changes from rev1: > ------------------ > 1. Move queue_index from virtio_pci_vq_info to virtqueue, > and resulting changes to existing code and to the patch. > 2. virtio-net probe uses virtio_config_val. > 3. Remove constants: VIRTIO_MAX_TXQS, MAX_VQS, all arrays > allocated on stack, etc. > 4. Restrict number of vhost threads to 2 - I get much better > cpu/sd results (without any tuning) with low number of vhost > threads. Higher vhosts gives better average BW performance > (from average of 45%), but SD increases significantly (90%). > 5. Working of vhost threads changes, eg for numtxqs=4: > vhost-0: handles RX > vhost-1: handles TX[0] > vhost-0: handles TX[1] > vhost-1: handles TX[2] > vhost-0: handles TX[3] This doesn't look symmetrical. TCP flows that go via TX(1,3) use the same vhost thread for RX packets, whereas flows via TX(0,2) use a different vhost thread. Thanks Sridhar -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
