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xen-netback: Fix handling of skbs requiring too many slots
A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers the next BUG_ON a few lines down, as the packet consumes more slots than estimated. This patch introduces full_coalesce on the skb callback buffer, which is used in start_new_rx_buffer() to decide whether netback needs coalescing more aggresively. By doing that, no packet should need more than (XEN_NETIF_MAX_TX_SIZE + 1) / PAGE_SIZE data slots (excluding the optional GSO slot, it doesn't carry data, therefore irrelevant in this case), as the provided buffers are fully utilized. Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com> Cc: Paul Durrant <paul.durrant@citrix.com> Cc: Wei Liu <wei.liu2@citrix.com> Cc: Ian Campbell <ian.campbell@citrix.com> Cc: David Vrabel <david.vrabel@citrix.com> Reviewed-by: Paul Durrant <paul.durrant@gmail.com> Acked-by: Wei Liu <wei.liu2@citrix.com> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
parent
c531692073
commit
59ae9fc670
1 changed files with 25 additions and 11 deletions
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@ -163,7 +163,8 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
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* adding 'size' bytes to a buffer which currently contains 'offset'
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* bytes.
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*/
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static bool start_new_rx_buffer(int offset, unsigned long size, int head)
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static bool start_new_rx_buffer(int offset, unsigned long size, int head,
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bool full_coalesce)
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{
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/* simple case: we have completely filled the current buffer. */
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if (offset == MAX_BUFFER_OFFSET)
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@ -175,6 +176,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
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* (i) this frag would fit completely in the next buffer
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* and (ii) there is already some data in the current buffer
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* and (iii) this is not the head buffer.
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* and (iv) there is no need to fully utilize the buffers
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*
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* Where:
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* - (i) stops us splitting a frag into two copies
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@ -185,6 +187,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
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* by (ii) but is explicitly checked because
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* netfront relies on the first buffer being
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* non-empty and can crash otherwise.
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* - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS
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* slot
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*
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* This means we will effectively linearise small
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* frags but do not needlessly split large buffers
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@ -192,7 +196,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
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* own buffers as before.
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*/
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BUG_ON(size > MAX_BUFFER_OFFSET);
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if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
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if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head &&
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!full_coalesce)
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return true;
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return false;
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@ -227,6 +232,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
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return meta;
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}
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struct xenvif_rx_cb {
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int meta_slots_used;
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bool full_coalesce;
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};
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#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
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/*
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* Set up the grant operations for this fragment. If it's a flipping
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* interface, we also set up the unmap request from here.
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@ -261,7 +273,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
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if (bytes > size)
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bytes = size;
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if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
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if (start_new_rx_buffer(npo->copy_off,
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bytes,
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*head,
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XENVIF_RX_CB(skb)->full_coalesce)) {
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/*
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* Netfront requires there to be some data in the head
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* buffer.
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@ -541,12 +556,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
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}
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}
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struct xenvif_rx_cb {
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int meta_slots_used;
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};
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#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
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void xenvif_kick_thread(struct xenvif *vif)
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{
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wake_up(&vif->wq);
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@ -602,10 +611,15 @@ static void xenvif_rx_action(struct xenvif *vif)
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/* To avoid the estimate becoming too pessimal for some
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* frontends that limit posted rx requests, cap the estimate
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* at MAX_SKB_FRAGS.
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* at MAX_SKB_FRAGS. In this case netback will fully coalesce
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* the skb into the provided slots.
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*/
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if (max_slots_needed > MAX_SKB_FRAGS)
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if (max_slots_needed > MAX_SKB_FRAGS) {
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max_slots_needed = MAX_SKB_FRAGS;
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XENVIF_RX_CB(skb)->full_coalesce = true;
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} else {
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XENVIF_RX_CB(skb)->full_coalesce = false;
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}
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/* We may need one more slot for GSO metadata */
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if (skb_is_gso(skb) &&
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