@@ -251,7 +251,6 @@ struct xenvif {
struct xenvif_rx_cb {
unsigned long expires;
int meta_slots_used;
- bool full_coalesce;
};
#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
@@ -233,51 +233,6 @@ static void xenvif_rx_queue_drop_expired(struct xenvif_queue *queue)
}
}
-/*
- * Returns true if we should start a new receive buffer instead of
- * adding 'size' bytes to a buffer which currently contains 'offset'
- * bytes.
- */
-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)
- return true;
-
- /*
- * complex case: start a fresh buffer if the current frag
- * would overflow the current buffer but only if:
- * (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
- * unless the frag is too large for a single buffer.
- * - (ii) stops us from leaving a buffer pointlessly empty.
- * - (iii) stops us leaving the first buffer
- * empty. Strictly speaking this is already covered
- * 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
- * into multiple copies tend to give large frags their
- * own buffers as before.
- */
- BUG_ON(size > MAX_BUFFER_OFFSET);
- if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head &&
- !full_coalesce)
- return true;
-
- return false;
-}
-
struct netrx_pending_operations {
unsigned copy_prod, copy_cons;
unsigned meta_prod, meta_cons;
@@ -336,24 +291,13 @@ static void xenvif_gop_frag_copy(struct xenvif_queue *queue, struct sk_buff *skb
BUG_ON(offset >= PAGE_SIZE);
BUG_ON(npo->copy_off > MAX_BUFFER_OFFSET);
- bytes = PAGE_SIZE - offset;
+ if (npo->copy_off == MAX_BUFFER_OFFSET)
+ meta = get_next_rx_buffer(queue, npo);
+ bytes = PAGE_SIZE - offset;
if (bytes > size)
bytes = size;
- 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.
- */
- BUG_ON(*head);
-
- meta = get_next_rx_buffer(queue, npo);
- }
-
if (npo->copy_off + bytes > MAX_BUFFER_OFFSET)
bytes = MAX_BUFFER_OFFSET - npo->copy_off;
@@ -652,60 +596,16 @@ static void xenvif_rx_action(struct xenvif_queue *queue)
while (xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX)
&& (skb = xenvif_rx_dequeue(queue)) != NULL) {
- RING_IDX max_slots_needed;
RING_IDX old_req_cons;
RING_IDX ring_slots_used;
int i;
queue->last_rx_time = jiffies;
- /* We need a cheap worse case estimate for the number of
- * slots we'll use.
- */
-
- max_slots_needed = DIV_ROUND_UP(offset_in_page(skb->data) +
- skb_headlen(skb),
- PAGE_SIZE);
- for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
- unsigned int size;
- unsigned int offset;
-
- size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
- offset = skb_shinfo(skb)->frags[i].page_offset;
-
- /* For a worse-case estimate we need to factor in
- * the fragment page offset as this will affect the
- * number of times xenvif_gop_frag_copy() will
- * call start_new_rx_buffer().
- */
- max_slots_needed += DIV_ROUND_UP(offset + size,
- PAGE_SIZE);
- }
-
- /* To avoid the estimate becoming too pessimal for some
- * frontends that limit posted rx requests, cap the estimate
- * at MAX_SKB_FRAGS. In this case netback will fully coalesce
- * the skb into the provided slots.
- */
- 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) &&
- (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
- skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6))
- max_slots_needed++;
-
old_req_cons = queue->rx.req_cons;
XENVIF_RX_CB(skb)->meta_slots_used = xenvif_gop_skb(skb, &npo, queue);
ring_slots_used = queue->rx.req_cons - old_req_cons;
- BUG_ON(ring_slots_used > max_slots_needed);
-
__skb_queue_tail(&rxq, skb);
}
Always fully coalesce guest Rx packets into the minimum number of ring slots. Reducing the number of slots per packet has significant performance benefits when receiving off-host traffic. Results from XenServer's performance benchmarks: Baseline Full coalesce Interhost VM receive 7.2 Gb/s 11 Gb/s Interhost aggregate 24 Gb/s 24 Gb/s Intrahost single stream 14 Gb/s 14 Gb/s Intrahost aggregate 34 Gb/s 34 Gb/s However, this can increase the number of grant ops per packet which decreases performance of backend (dom0) to VM traffic (by ~10%) /unless/ grant copy has been optimized for adjacent ops with the same source or destination (see "grant-table: defer releasing pages acquired in a grant copy"[1] expected in Xen 4.6). [1] http://lists.xen.org/archives/html/xen-devel/2015-01/msg01118.html Signed-off-by: David Vrabel <david.vrabel@citrix.com> Acked-by: Ian Campbell <ian.campbell@citrix.com> --- Changes in v2: - Updated commit message with better results. drivers/net/xen-netback/common.h | 1 - drivers/net/xen-netback/netback.c | 106 ++----------------------------------- 2 files changed, 3 insertions(+), 104 deletions(-)