3.16.72-rc1 review patch. If anyone has any objections, please let me know.
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From: Paolo Abeni pabeni@redhat.com
commit db688c24eada63b1efe6d0d7d835e5c3bdd71fd3 upstream.
Similar to commit a2ac99905f1e ("vhost-net: set packet weight of tx polling to 2 * vq size"), we need a packet-based limit for handler_rx, too - elsewhere, under rx flood with small packets, tx can be delayed for a very long time, even without busypolling.
The pkt limit applied to handle_rx must be the same applied by handle_tx, or we will get unfair scheduling between rx and tx. Tying such limit to the queue length makes it less effective for large queue length values and can introduce large process scheduler latencies, so a constant valued is used - likewise the existing bytes limit.
The selected limit has been validated with PVP[1] performance test with different queue sizes:
queue size 256 512 1024
baseline 366 354 362 weight 128 715 723 670 weight 256 740 745 733 weight 512 600 460 583 weight 1024 423 427 418
A packet weight of 256 gives peek performances in under all the tested scenarios.
No measurable regression in unidirectional performance tests has been detected.
[1] https://developers.redhat.com/blog/2017/06/05/measuring-and-comparing-open-v...
Signed-off-by: Paolo Abeni pabeni@redhat.com Acked-by: Jason Wang jasowang@redhat.com Signed-off-by: David S. Miller davem@davemloft.net [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/vhost/net.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
--- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -40,8 +40,10 @@ MODULE_PARM_DESC(experimental_zcopytx, " #define VHOST_NET_WEIGHT 0x80000
/* Max number of packets transferred before requeueing the job. - * Using this limit prevents one virtqueue from starving rx. */ -#define VHOST_NET_PKT_WEIGHT(vq) ((vq)->num * 2) + * Using this limit prevents one virtqueue from starving others with small + * pkts. + */ +#define VHOST_NET_PKT_WEIGHT 256
/* MAX number of TX used buffers for outstanding zerocopy */ #define VHOST_MAX_PEND 128 @@ -456,7 +458,7 @@ static void handle_tx(struct vhost_net * total_len += len; vhost_net_tx_packet(net); if (unlikely(total_len >= VHOST_NET_WEIGHT) || - unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT(vq))) { + unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT)) { vhost_poll_queue(&vq->poll); break; } @@ -581,6 +583,7 @@ static void handle_rx(struct vhost_net * size_t vhost_hlen, sock_hlen; size_t vhost_len, sock_len; struct socket *sock; + int recv_pkts = 0;
mutex_lock(&vq->mutex); sock = vq->private_data; @@ -665,7 +668,8 @@ static void handle_rx(struct vhost_net * if (unlikely(vq_log)) vhost_log_write(vq, vq_log, log, vhost_len); total_len += vhost_len; - if (unlikely(total_len >= VHOST_NET_WEIGHT)) { + if (unlikely(total_len >= VHOST_NET_WEIGHT) || + unlikely(++recv_pkts >= VHOST_NET_PKT_WEIGHT)) { vhost_poll_queue(&vq->poll); break; }