From: Jason Wang Date: Tue, 9 Jan 2018 10:27:45 +0000 (+0800) Subject: vhost_net: batch used ring update in rx X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=e2b3b35eb989;p=openwrt%2Fstaging%2Fblogic.git vhost_net: batch used ring update in rx This patch tries to batched used ring update during RX. This is pretty fit for the case when guest is much faster (e.g dpdk based backend). In this case, used ring is almost empty: - we may get serious cache line misses/contending on both used ring and used idx. - at most 1 packet could be dequeued at one time, batching in guest does not make much effect. Update used ring in a batch can help since guest won't access the used ring until used idx was advanced for several descriptors and since we advance used ring for every N packets, guest will only need to access used idx for every N packet since it can cache the used idx. To have a better interaction for both batch dequeuing and dpdk batching, VHOST_RX_BATCH was used as the maximum number of descriptors that could be batched. Test were done between two machines with 2.40GHz Intel(R) Xeon(R) CPU E5-2630 connected back to back through ixgbe. Traffic were generated on one remote ixgbe through MoonGen and measure the RX pps through testpmd in guest when do xdp_redirect_map from local ixgbe to tap. RX pps were increased from 3.05 Mpps to 4.00 Mpps (about 31% improvement). One possible concern for this is the implications for TCP (especially latency sensitive workload). Result[1] does not show obvious changes for most of the netperf test (RR, TX, and RX). And we do get some improvements for RX on some specific size. Guest RX: size/sessions/+thu%/+normalize% 64/ 1/ +2%/ +2% 64/ 2/ +2%/ -1% 64/ 4/ +1%/ +1% 64/ 8/ 0%/ 0% 256/ 1/ +6%/ -3% 256/ 2/ -3%/ +2% 256/ 4/ +11%/ +11% 256/ 8/ 0%/ 0% 512/ 1/ +4%/ 0% 512/ 2/ +2%/ +2% 512/ 4/ 0%/ -1% 512/ 8/ -8%/ -8% 1024/ 1/ -7%/ -17% 1024/ 2/ -8%/ -7% 1024/ 4/ +1%/ 0% 1024/ 8/ 0%/ 0% 2048/ 1/ +30%/ +14% 2048/ 2/ +46%/ +40% 2048/ 4/ 0%/ 0% 2048/ 8/ 0%/ 0% 4096/ 1/ +23%/ +22% 4096/ 2/ +26%/ +23% 4096/ 4/ 0%/ +1% 4096/ 8/ 0%/ 0% 16384/ 1/ -2%/ -3% 16384/ 2/ +1%/ -4% 16384/ 4/ -1%/ -3% 16384/ 8/ 0%/ -1% 65535/ 1/ +15%/ +7% 65535/ 2/ +4%/ +7% 65535/ 4/ 0%/ +1% 65535/ 8/ 0%/ 0% TCP_RR: size/sessions/+thu%/+normalize% 1/ 1/ 0%/ +1% 1/ 25/ +2%/ +1% 1/ 50/ +4%/ +1% 64/ 1/ 0%/ -4% 64/ 25/ +2%/ +1% 64/ 50/ 0%/ -1% 256/ 1/ 0%/ 0% 256/ 25/ 0%/ 0% 256/ 50/ +4%/ +2% Guest TX: size/sessions/+thu%/+normalize% 64/ 1/ +4%/ -2% 64/ 2/ -6%/ -5% 64/ 4/ +3%/ +6% 64/ 8/ 0%/ +3% 256/ 1/ +15%/ +16% 256/ 2/ +11%/ +12% 256/ 4/ +1%/ 0% 256/ 8/ +5%/ +5% 512/ 1/ -1%/ -6% 512/ 2/ 0%/ -8% 512/ 4/ -2%/ +4% 512/ 8/ +6%/ +9% 1024/ 1/ +3%/ +1% 1024/ 2/ +3%/ +9% 1024/ 4/ 0%/ +7% 1024/ 8/ 0%/ +7% 2048/ 1/ +8%/ +2% 2048/ 2/ +3%/ -1% 2048/ 4/ -1%/ +11% 2048/ 8/ +3%/ +9% 4096/ 1/ +8%/ +8% 4096/ 2/ 0%/ -7% 4096/ 4/ +4%/ +4% 4096/ 8/ +2%/ +5% 16384/ 1/ -3%/ +1% 16384/ 2/ -1%/ -12% 16384/ 4/ -1%/ +5% 16384/ 8/ 0%/ +1% 65535/ 1/ 0%/ -3% 65535/ 2/ +5%/ +16% 65535/ 4/ +1%/ +2% 65535/ 8/ +1%/ -1% Signed-off-by: Jason Wang Acked-by: Michael S. Tsirkin Signed-off-by: David S. Miller --- diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index a5a1db647635..7baa90abe097 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -756,7 +756,7 @@ static void handle_rx(struct vhost_net *net) }; size_t total_len = 0; int err, mergeable; - s16 headcount; + s16 headcount, nheads = 0; size_t vhost_hlen, sock_hlen; size_t vhost_len, sock_len; struct socket *sock; @@ -784,7 +784,7 @@ static void handle_rx(struct vhost_net *net) while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk))) { sock_len += sock_hlen; vhost_len = sock_len + vhost_hlen; - headcount = get_rx_bufs(vq, vq->heads, vhost_len, + headcount = get_rx_bufs(vq, vq->heads + nheads, vhost_len, &in, vq_log, &log, likely(mergeable) ? UIO_MAXIOV : 1); /* On error, stop handling until the next kick. */ @@ -856,8 +856,12 @@ static void handle_rx(struct vhost_net *net) vhost_discard_vq_desc(vq, headcount); goto out; } - vhost_add_used_and_signal_n(&net->dev, vq, vq->heads, - headcount); + nheads += headcount; + if (nheads > VHOST_RX_BATCH) { + vhost_add_used_and_signal_n(&net->dev, vq, vq->heads, + nheads); + nheads = 0; + } if (unlikely(vq_log)) vhost_log_write(vq, vq_log, log, vhost_len); total_len += vhost_len; @@ -868,6 +872,9 @@ static void handle_rx(struct vhost_net *net) } vhost_net_enable_vq(net, vq); out: + if (nheads) + vhost_add_used_and_signal_n(&net->dev, vq, vq->heads, + nheads); mutex_unlock(&vq->mutex); }