netvsc: optimize calculation of number of slots

Speed up transmit check for fragmented packets by using existing
macros to compute number of pages, and eliminate loop since
skb fragments each take a page. Number of slots is also unsigned.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc_drv.c

@@ -345,34 +345,14 @@ static u32 init_page_array(void *hdr, u32 len, struct sk_buff *skb,
 	return slots_used;
 }
 
-static int count_skb_frag_slots(struct sk_buff *skb)
-{
-	int i, frags = skb_shinfo(skb)->nr_frags;
-	int pages = 0;
-
-	for (i = 0; i < frags; i++) {
-		skb_frag_t *frag = skb_shinfo(skb)->frags + i;
-		unsigned long size = skb_frag_size(frag);
-		unsigned long offset = frag->page_offset;
-
-		/* Skip unused frames from start of page */
-		offset &= ~PAGE_MASK;
-		pages += PFN_UP(offset + size);
-	}
-	return pages;
-}
-
-static int netvsc_get_slots(struct sk_buff *skb)
+/* Estimate number of page buffers neede to transmit
+ * Need at most 2 for RNDIS header plus skb body and fragments.
+ */
+static unsigned int netvsc_get_slots(const struct sk_buff *skb)
 {
-	char *data = skb->data;
-	unsigned int offset = offset_in_page(data);
-	unsigned int len = skb_headlen(skb);
-	int slots;
-	int frag_slots;
-
-	slots = DIV_ROUND_UP(offset + len, PAGE_SIZE);
-	frag_slots = count_skb_frag_slots(skb);
-	return slots + frag_slots;
+	return PFN_UP(offset_in_page(skb->data) + skb_headlen(skb))
+		+ skb_shinfo(skb)->nr_frags
+		+ 2;
 }
 
 static u32 net_checksum_info(struct sk_buff *skb)
@@ -410,21 +390,18 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	struct hv_page_buffer page_buf[MAX_PAGE_BUFFER_COUNT];
 	struct hv_page_buffer *pb = page_buf;
 
-	/* We will atmost need two pages to describe the rndis
-	 * header. We can only transmit MAX_PAGE_BUFFER_COUNT number
+	/* We can only transmit MAX_PAGE_BUFFER_COUNT number
 	 * of pages in a single packet. If skb is scattered around
 	 * more pages we try linearizing it.
 	 */
-
-	num_data_pgs = netvsc_get_slots(skb) + 2;
-
+	num_data_pgs = netvsc_get_slots(skb);
 	if (unlikely(num_data_pgs > MAX_PAGE_BUFFER_COUNT)) {
 		++net_device_ctx->eth_stats.tx_scattered;
 
 		if (skb_linearize(skb))
 			goto no_memory;
 
-		num_data_pgs = netvsc_get_slots(skb) + 2;
+		num_data_pgs = netvsc_get_slots(skb);
 		if (num_data_pgs > MAX_PAGE_BUFFER_COUNT) {
 			++net_device_ctx->eth_stats.tx_too_big;
 			goto drop;