Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 59ae9fc6 authored by Zoltan Kiss's avatar Zoltan Kiss Committed by David S. Miller
Browse files

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: default avatarZoltan 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: default avatarPaul Durrant <paul.durrant@gmail.com>
Acked-by: default avatarWei Liu <wei.liu2@citrix.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c5316920

drivers/net/xen-netback/netback.c

+25 −11
Original line number Diff line number Diff line
@@ -163,7 +163,8 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed) 
 * adding 'size' bytes to a buffer which currently contains 'offset'

 * bytes.

 */

static bool start_new_rx_buffer(int offset, unsigned long size, int head)

static bool start_new_rx_buffer(int offset, unsigned long size, int head,

				bool full_coalesce)

{

	/* simple case: we have completely filled the current buffer. */

	if (offset == MAX_BUFFER_OFFSET)
@@ -175,6 +176,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head) 
	 *     (i)   this frag would fit completely in the next buffer

	 * and (ii)  there is already some data in the current buffer

	 * and (iii) this is not the head buffer.

	 * and (iv)  there is no need to fully utilize the buffers

	 *

	 * Where:

	 * - (i) stops us splitting a frag into two copies
@@ -185,6 +187,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head) 
	 *   by (ii) but is explicitly checked because

	 *   netfront relies on the first buffer being

	 *   non-empty and can crash otherwise.

	 * - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS

	 *   slot

	 *

	 * This means we will effectively linearise small

	 * frags but do not needlessly split large buffers
@@ -192,7 +196,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head) 
	 * own buffers as before.

	 */

	BUG_ON(size > MAX_BUFFER_OFFSET);

	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)

	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head &&

	    !full_coalesce)

		return true;



	return false;
@@ -227,6 +232,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif, 
	return meta;

}



struct xenvif_rx_cb {

	int meta_slots_used;

	bool full_coalesce;

};



#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)



/*

 * Set up the grant operations for this fragment. If it's a flipping

 * interface, we also set up the unmap request from here.
@@ -261,7 +273,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb, 
		if (bytes > size)

			bytes = size;



		if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {

		if (start_new_rx_buffer(npo->copy_off,

					bytes,

					*head,

					XENVIF_RX_CB(skb)->full_coalesce)) {

			/*

			 * Netfront requires there to be some data in the head

			 * buffer.
@@ -541,12 +556,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status, 
	}

}



struct xenvif_rx_cb {

	int meta_slots_used;

};



#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)



void xenvif_kick_thread(struct xenvif *vif)

{

	wake_up(&vif->wq);
@@ -602,10 +611,15 @@ static void xenvif_rx_action(struct xenvif *vif) 


		/* To avoid the estimate becoming too pessimal for some

		 * frontends that limit posted rx requests, cap the estimate

		 * at MAX_SKB_FRAGS.

		 * at MAX_SKB_FRAGS. In this case netback will fully coalesce

		 * the skb into the provided slots.

		 */

		if (max_slots_needed > MAX_SKB_FRAGS)

		if (max_slots_needed > MAX_SKB_FRAGS) {

			max_slots_needed = MAX_SKB_FRAGS;

			XENVIF_RX_CB(skb)->full_coalesce = true;

		} else {

			XENVIF_RX_CB(skb)->full_coalesce = false;

		}



		/* We may need one more slot for GSO metadata */

		if (skb_is_gso(skb) &&