Re: [PATCH net-next] vhost_net: stop rx net polling when possible
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2014-08-17 10:20:27
Also in:
kvm, lkml, virtualization
On Fri, Aug 15, 2014 at 11:40:08AM +0800, Jason Wang wrote:
After rx vq was enabled, we never stop polling its socket. This is sub optimal when may lead unnecessary wake-ups after the rx net work has already been queued. This could be optimized by stopping polling the rx net sock when processing both rx and tx and restart it afterward. This could save unnecessary wake-ups and even unnecessary spin locks acquiring with the help of commit 9e641bdcfa4ef4d6e2fbaa59c1be0ad5d1551fd5 "net-tun: restructure tun_do_read for better sleep/wakeup efficiency".
OK so the point is to avoid expensive wake_up_process calls? It's a bit unfortunate that we are adding/removing things from wait queue which certainly does take extra spin-locks.
Test shows significant CPU% savings during almost all the cases: Guest rx stream: size(B)/sessions/throughput/cpu/normalized thru/ 64/1/+0.7773% -8.6224% +10.2866% 64/2/+0.6335% -13.9109% +16.8946% 64/4/-0.8182% -14.8336% +16.4565% 64/8/+0.4830% -13.7675% +16.5256% 256/1/-7.0963% -12.6880% +6.4043% 256/2/-1.3982% -11.5424% +11.4678% 256/4/-0.0350% -11.8323% +13.3806% 256/8/-1.5830% -12.7693% +12.8238% 1024/1/-7.4895% -19.1449% +14.4152% 1024/2/-7.4575% -19.4018% +14.8195% 1024/4/-0.3881% -9.1183% +9.6061% 1024/8/+0.4713% -11.0155% +12.9087% 4096/1/+0.8786% -8.4050% +10.1355% 4096/2/+0.0098% -15.3094% +18.0885% 4096/4/+0.0445% -10.8247% +12.1886% 4096/8/-2.1317% -12.5111% +11.8637% 16384/1/-0.0008% -6.1891% +6.5966% 16384/2/-0.0117% -16.2716% +19.4198% 16384/4/+0.0001% -5.9197% +6.2923% 16384/8/+0.0173% -7.6681% +8.3236% 65535/1/+0.0011% -10.3594% +11.5578% 65535/2/-0.4108% -14.4304% +16.3838% 65535/4/+0.0011% -10.3594% +11.5578% 65535/8/-0.4108% -14.4304% +16.3838% Guest tx stream: size(B)/sessions/throughput/cpu/normalized thru/ 64/1/-0.6228% -2.1936% +1.6060% 64/2/+0.8646% -3.5063% +4.5297% 64/4/+0.8733% -3.2495% +4.2613% 64/8/+1.4290% -3.5593% +5.1724% 256/1/+7.2098% -3.1122% +10.6535% 256/2/-10.1408% -6.8230% -3.5607% 256/4/-11.3531% -6.7085% -4.9785% 256/8/-10.2723% -6.5628% -3.9701% 1024/1/-18.9329% -13.6162% -6.1547% 1024/2/-0.3728% -1.3181% +0.9580% 1024/4/+0.0125% -3.6338% +3.7838% 1024/8/-0.0030% -2.7282% +2.8017% 4096/1/+16.9367% -1.9435% +19.2543% 4096/2/+0.0121% -6.1682% +6.5866% 4096/4/+0.0019% -3.8510% +4.0072% 4096/8/-0.0222% -4.1368% +4.2922% 16384/1/-0.0026% -8.6892% +9.5132% 16384/2/-0.0012% -10.1676% +11.3171% 16384/4/+0.0196% -1.2551% +1.2908% 16384/8/+0.1303% -3.2634% +3.5082% 65535/1/+0.0019% -3.4694% +3.5961% 65535/2/-0.0003% -0.7635% +0.7690% 65535/4/-0.0219% -2.7875% +2.8448% 65535/8/+0.1137% -2.7922% +2.9894% TCP_RR: size(B)/sessions/throughput/cpu/normalized thru/ 256/1/+1.9004% -4.7985% +7.0366% 256/25/-4.7366% -11.0809% +7.1349% 256/50/+3.9808% -5.2037% +9.6887% 4096/1/+2.1619% -0.7303% +2.9134% 4096/25/-13.1836% -14.7298% +1.8134% 4096/50/-11.1990% -15.4763% +5.0605% Signed-off-by: Jason Wang <redacted>
Could you split RX/TX parts out please, and benchmark separately? They are really independent.
quoted hunk ↗ jump to hunk
--- drivers/vhost/net.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 8dae2f7..d4a9742 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c@@ -334,6 +334,8 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) static void handle_tx(struct vhost_net *net) { struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX]; + struct vhost_virtqueue *rx_vq = &net->vqs[VHOST_NET_VQ_RX].vq; + struct vhost_poll *rx_poll = &net->poll[VHOST_NET_VQ_RX]; struct vhost_virtqueue *vq = &nvq->vq; unsigned out, in, s; int head;@@ -348,15 +350,18 @@ static void handle_tx(struct vhost_net *net) size_t len, total_len = 0; int err; size_t hdr_size; - struct socket *sock; + struct socket *sock, *rxsock; struct vhost_net_ubuf_ref *uninitialized_var(ubufs); - bool zcopy, zcopy_used; + bool zcopy, zcopy_used, poll = false; mutex_lock(&vq->mutex); + mutex_lock(&rx_vq->mutex); sock = vq->private_data; + rxsock = rx_vq->private_data; if (!sock) goto out; + vhost_poll_stop(rx_poll); vhost_disable_notify(&net->dev, vq); hdr_size = nvq->vhost_hlen;@@ -451,11 +456,17 @@ static void handle_tx(struct vhost_net *net) total_len += len; vhost_net_tx_packet(net); if (unlikely(total_len >= VHOST_NET_WEIGHT)) { - vhost_poll_queue(&vq->poll); + poll = true; break; } } + + if (rxsock) + vhost_poll_start(rx_poll, rxsock->file); + if (poll) + vhost_poll_queue(&vq->poll); out: + mutex_unlock(&rx_vq->mutex); mutex_unlock(&vq->mutex); }@@ -554,6 +565,7 @@ err: static void handle_rx(struct vhost_net *net) { struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_RX]; + struct vhost_poll *poll = &net->poll[VHOST_NET_VQ_RX]; struct vhost_virtqueue *vq = &nvq->vq; unsigned uninitialized_var(in), log; struct vhost_log *vq_log;@@ -580,6 +592,8 @@ static void handle_rx(struct vhost_net *net) sock = vq->private_data; if (!sock) goto out; + + vhost_poll_stop(poll); vhost_disable_notify(&net->dev, vq); vhost_hlen = nvq->vhost_hlen;@@ -660,10 +674,12 @@ static void handle_rx(struct vhost_net *net) vhost_log_write(vq, vq_log, log, vhost_len); total_len += vhost_len; if (unlikely(total_len >= VHOST_NET_WEIGHT)) { - vhost_poll_queue(&vq->poll); - break; + vhost_poll_queue(poll); + goto out; } } + + vhost_poll_start(poll, sock->file); out: mutex_unlock(&vq->mutex); }-- 1.9.1