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Re: [Xen-devel] [PATCH net] xen-netback: Fix slot estimation
On 03/06/14 14:52, David Laight wrote:
From: netdev-owner@xxxxxxxxxxxxxxx
@@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
/* If the skb may not fit then bail out now */
if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
+ /* If the skb needs more than MAX_SKB_FRAGS slots, it
+ * can happen that the frontend never gives us enough.
+ * To avoid spining on that packet, first we put it back
+ * to the top of the queue, but if the next try fail,
+ * we drop it.
+ */
+ if (max_slots_needed > MAX_SKB_FRAGS &&
+ vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
+ kfree_skb(skb);
+ vif->rx_last_skb_slots = 0;
+ continue;
+ }
A silent discard here doesn't seem right at all.
While it stops the kernel crashing, or the entire interface locking
up; it is likely to leave one connection 'stuck' - a TCP retransmission
is likely to include the same fragments.
From a user point of view this as almost as bad.
Yes, we are aware of this problem for a while. However I have an idea to
solve that in a way that we don't lose performance, and these packets
can pass through as well. See my patch called "Fix handling of skbs
requiring too many slots"
Zoli
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