Hello all: We free old transmitted packets in ndo_start_xmit() currently, so any packet must be orphaned also there. This was used to reduce the overhead of tx interrupt to achieve better performance. But this may not work for some protocols such as TCP stream. TCP depends on the value of sk_wmem_alloc to implement various optimization for small packets stream such as TCP small queue and auto corking. But orphaning packets early in ndo_start_xmit() disable such things more or less since sk_wmem_alloc was not accurate. This lead extra low throughput for TCP stream of small writes. This series tries to solve this issue by enable tx interrupts for all TCP packets other than the ones with push bit or pure ACK. This is done through the support of urgent descriptor which can force an interrupt for a specified packet. If tx interrupt was enabled for a packet, there's no need to orphan it in ndo_start_xmit(), we can free it tx napi which is scheduled by tx interrupt. Then sk_wmem_alloc was more accurate than before and TCP can batch more for small write. More larger skb was produced by TCP in this case to improve both throughput and cpu utilization. Test shows great improvements on small write tcp streams. For most of the other cases, the throughput and cpu utilization are the same in the past. Only few cases, more cpu utilization was noticed which needs more investigation. Review and comments are welcomed. Thanks Test result: - Two Intel Corporation Xeon 5600s (8 cores) with back to back connected 82599ES: - netperf test between guest and remote host - 1 queue 2 vcpus with zercopy enabled vhost_net - both host and guest are net-next.git with the patches. - Value with '[]' means obvious difference (the significance is greater than 95%). - he significance of the differences between the two averages is calculated using unpaired T-test that takes into account the SD of the averages. Guest RX size/sessions/throughput-+%/cpu-+%/per cpu throughput -+%/ 64/1/+3.7872%/+3.2307%/+0.5390%/ 64/2/-0.2325%/+2.9552%/-3.0962%/ 64/4/[-2.0296%]/+2.2955%/[-4.2280%]/ 64/8/+0.0944%/[+2.2654%]/-2.4662%/ 256/1/+1.1947%/-2.5462%/+3.8386%/ 256/2/-1.6477%/+3.4421%/-4.9301%/ 256/4/[-5.9526%]/[+6.8861%]/[-11.9951%]/ 256/8/-3.6470%/-1.5887%/-2.0916%/ 1024/1/-4.2225%/-1.3238%/-2.9376%/ 1024/2/+0.3568%/+1.8439%/-1.4601%/ 1024/4/-0.7065%/-0.0099%/-2.3483%/ 1024/8/-1.8620%/-2.4774%/+0.6310%/ 4096/1/+0.0115%/-0.3693%/+0.3823%/ 4096/2/-0.0209%/+0.8730%/-0.8862%/ 4096/4/+0.0729%/-7.0303%/+7.6403%/ 4096/8/-2.3720%/+0.0507%/-2.4214%/ 16384/1/+0.0222%/-1.8672%/+1.9254%/ 16384/2/+0.0986%/+3.2968%/-3.0961%/ 16384/4/-1.2059%/+7.4291%/-8.0379%/ 16384/8/-1.4893%/+0.3403%/-1.8234%/ 65535/1/-0.0445%/-1.4060%/+1.3808%/ 65535/2/-0.0311%/+0.9610%/-0.9827%/ 65535/4/-0.7015%/+0.3660%/-1.0637%/ 65535/8/-3.1585%/+11.1302%/[-12.8576%]/ Guest TX size/sessions/throughput-+%/cpu-+%/per cpu throughput -+%/ 64/1/[+75.2622%]/[-14.3928%]/[+104.7283%]/ 64/2/[+68.9596%]/[-12.6655%]/[+93.4625%]/ 64/4/[+68.0126%]/[-12.7982%]/[+92.6710%]/ 64/8/[+67.9870%]/[-12.6297%]/[+92.2703%]/ 256/1/[+160.4177%]/[-26.9643%]/[+256.5624%]/ 256/2/[+48.4357%]/[-24.3380%]/[+96.1825%]/ 256/4/[+48.3663%]/[-24.1127%]/[+95.5087%]/ 256/8/[+47.9722%]/[-24.2516%]/[+95.3469%]/ 1024/1/[+54.4474%]/[-52.9223%]/[+228.0694%]/ 1024/2/+0.0742%/[-12.7444%]/[+14.6908%]/ 1024/4/[+0.5524%]/-0.0327%/+0.5853%/ 1024/8/[-1.2783%]/[+6.2902%]/[-7.1206%]/ 4096/1/+0.0778%/-13.1121%/+15.1804%/ 4096/2/+0.0189%/[-11.3176%]/[+12.7832%]/ 4096/4/+0.0218%/-1.0389%/+1.0718%/ 4096/8/-1.3774%/[+12.7396%]/[-12.5218%]/ 16384/1/+0.0136%/-2.5043%/+2.5826%/ 16384/2/+0.0509%/[-15.3846%]/[+18.2420%]/ 16384/4/-0.0163%/[-4.8808%]/[+5.1141%]/ 16384/8/[-1.7249%]/[+13.9174%]/[-13.7313%]/ 65535/1/+0.0686%/-5.4942%/+5.8862%/ 65535/2/+0.0043%/[-7.5816%]/[+8.2082%]/ 65535/4/+0.0080%/[-7.2993%]/[+7.8827%]/ 65535/8/[-1.3669%]/[+16.6536%]/[-15.4479%]/ Guest TCP_RR size/sessions/throughput-+%/cpu-+%/per cpu throughput -+%/ 256/1/-0.2914%/+12.6457%/-11.4848%/ 256/25/-0.5968%/-5.0531%/+4.6935%/ 256/50/+0.0262%/+0.2079%/-0.1813%/ 4096/1/+2.6965%/[+16.1248%]/[-11.5636%]/ 4096/25/-0.5002%/+0.5449%/-1.0395%/ 4096/50/[-2.0987%]/-0.0330%/[-2.0664%]/ Tests on mlx4 was ongoing, will post the result in next week. Jason Wang (3): virtio: support for urgent descriptors vhost: support urgent descriptors virtio-net: conditionally enable tx interrupt drivers/net/virtio_net.c | 164 ++++++++++++++++++++++++++++++--------- drivers/vhost/net.c | 43 +++++++--- drivers/vhost/scsi.c | 23 ++++-- drivers/vhost/test.c | 5 +- drivers/vhost/vhost.c | 44 +++++++---- drivers/vhost/vhost.h | 19 +++-- drivers/virtio/virtio_ring.c | 75 +++++++++++++++++- include/linux/virtio.h | 14 ++++ include/uapi/linux/virtio_ring.h | 5 +- 9 files changed, 308 insertions(+), 84 deletions(-) -- 1.8.3.1 -- 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
