netdev - [PATCH V2 2/6] vhost_net: use vhost_add_used_and_signal_n() in vhost_zerocopy_signal

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Message-Id: <1377836962-49780-3-git-send-email-jasowang@redhat.com>
Date:	Fri, 30 Aug 2013 12:29:18 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	mst@...hat.com, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	Jason Wang <jasowang@...hat.com>
Subject: [PATCH V2 2/6] vhost_net: use vhost_add_used_and_signal_n() in vhost_zerocopy_signal_used()

We tend to batch the used adding and signaling in vhost_zerocopy_callback()
which may result more than 100 used buffers to be updated in
vhost_zerocopy_signal_used() in some cases. So wwitch to use
vhost_add_used_and_signal_n() to avoid multiple calls to
vhost_add_used_and_signal(). Which means much more less times of used index
updating and memory barriers.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/vhost/net.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 280ee66..8a6dd0d 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -281,7 +281,7 @@ static void vhost_zerocopy_signal_used(struct vhost_net *net,
 {
 	struct vhost_net_virtqueue *nvq =
 		container_of(vq, struct vhost_net_virtqueue, vq);
-	int i;
+	int i, add;
 	int j = 0;
 
 	for (i = nvq->done_idx; i != nvq->upend_idx; i = (i + 1) % UIO_MAXIOV) {
@@ -289,14 +289,17 @@ static void vhost_zerocopy_signal_used(struct vhost_net *net,
 			vhost_net_tx_err(net);
 		if (VHOST_DMA_IS_DONE(vq->heads[i].len)) {
 			vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
-			vhost_add_used_and_signal(vq->dev, vq,
-						  vq->heads[i].id, 0);
 			++j;
 		} else
 			break;
 	}
-	if (j)
-		nvq->done_idx = i;
+	while (j) {
+		add = min(UIO_MAXIOV - nvq->done_idx, j);
+		vhost_add_used_and_signal_n(vq->dev, vq,
+					    &vq->heads[nvq->done_idx], add);
+		nvq->done_idx = (nvq->done_idx + add) % UIO_MAXIOV;
+		j -= add;
+	}
 }
 
 static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
-- 
1.7.1

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