netdev - [PATCH net-next 1/3] netvsc: optimize calculation of number of slots

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Date:   Mon, 29 May 2017 11:31:57 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, Stephen Hemminger <sthemmin@...rosoft.com>
Subject: [PATCH net-next 1/3] 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
each skb fragment is only one page.

Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>
---
 drivers/net/hyperv/netvsc_drv.c | 43 ++++++++++-------------------------------
 1 file changed, 10 insertions(+), 33 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 4421a6d00375..548c78863ce9 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -343,34 +343,14 @@ 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)
@@ -408,21 +388,18 @@ 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;
-- 
2.11.0