netdev - [PATCHv1 net] xen-netback: use skb to determine number of required guest Rx requests

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Message-ID: <1452784710-11923-1-git-send-email-david.vrabel@citrix.com>
Date:	Thu, 14 Jan 2016 15:18:30 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	<netdev@...r.kernel.org>
CC:	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>
Subject: [PATCHv1 net] xen-netback: use skb to determine number of required guest Rx requests

Using the MTU or GSO size to determine the number of required guest Rx
requests for an skb was subtly broken since these value may change at
runtime.

Signed-off-by: David Vrabel <david.vrabel@...rix.com>
---
 drivers/net/xen-netback/netback.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 1049c34..61b97c3 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -149,20 +149,19 @@ static inline pending_ring_idx_t pending_index(unsigned i)
 	return i & (MAX_PENDING_REQS-1);
 }
 
-static int xenvif_rx_ring_slots_needed(struct xenvif *vif)
-{
-	if (vif->gso_mask)
-		return DIV_ROUND_UP(vif->dev->gso_max_size, XEN_PAGE_SIZE) + 1;
-	else
-		return DIV_ROUND_UP(vif->dev->mtu, XEN_PAGE_SIZE);
-}
-
 static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
 {
 	RING_IDX prod, cons;
+	struct sk_buff *skb;
 	int needed;
 
-	needed = xenvif_rx_ring_slots_needed(queue->vif);
+	skb = skb_peek(&queue->rx_queue);
+	if (!skb)
+		return false;
+
+	needed = DIV_ROUND_UP(skb->len, XEN_PAGE_SIZE);
+	if (skb_is_gso(skb))
+		needed++;
 
 	do {
 		prod = queue->rx.sring->req_prod;
@@ -2005,8 +2004,7 @@ static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
 
 static bool xenvif_have_rx_work(struct xenvif_queue *queue)
 {
-	return (!skb_queue_empty(&queue->rx_queue)
-		&& xenvif_rx_ring_slots_available(queue))
+	return xenvif_rx_ring_slots_available(queue)
 		|| (queue->vif->stall_timeout &&
 		    (xenvif_rx_queue_stalled(queue)
 		     || xenvif_rx_queue_ready(queue)))
-- 
2.1.4