vhost_net: correctly limit the max pending buffers (f7c6be40) · Commits · 戴 / test

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 <jasowang@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

drivers/vhost/net.c

+7 −11

Original line number	Diff line number	Diff line
		@@ -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;

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