From f7c6be404d8fa52c54ff931390aab01e5c7654d6 Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Mon, 2 Sep 2013 16:41:01 +0800 Subject: [PATCH] vhost_net: correctly limit the max pending buffers As Michael point out, We used to limit the max pending DMAs to get better cache utilization. But it was not done correctly since it was one done when there's no new buffers submitted from guest. Guest can easily exceeds the limitation by keeping sending packets. So this patch moves the check into main loop. Tests shows about 5%-10% improvement on per cpu throughput for guest tx. Signed-off-by: Jason Wang Signed-off-by: David S. Miller --- drivers/vhost/net.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 8e9dc554b1ef..831eb4fd197d 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -363,6 +363,13 @@ static void handle_tx(struct vhost_net *net) if (zcopy) vhost_zerocopy_signal_used(net, vq); + /* If more outstanding DMAs, queue the work. + * Handle upend_idx wrap around + */ + if (unlikely((nvq->upend_idx + vq->num - VHOST_MAX_PEND) + % UIO_MAXIOV == nvq->done_idx)) + break; + head = vhost_get_vq_desc(&net->dev, vq, vq->iov, ARRAY_SIZE(vq->iov), &out, &in, @@ -372,17 +379,6 @@ static void handle_tx(struct vhost_net *net) break; /* Nothing new? Wait for eventfd to tell us they refilled. */ if (head == vq->num) { - int num_pends; - - /* If more outstanding DMAs, queue the work. - * Handle upend_idx wrap around - */ - num_pends = likely(nvq->upend_idx >= nvq->done_idx) ? - (nvq->upend_idx - nvq->done_idx) : - (nvq->upend_idx + UIO_MAXIOV - - nvq->done_idx); - if (unlikely(num_pends > VHOST_MAX_PEND)) - break; if (unlikely(vhost_enable_notify(&net->dev, vq))) { vhost_disable_notify(&net->dev, vq); continue; -- 2.20.1