hv_netvsc: use reciprocal divide to speed up percent calculation

Every packet sent checks the available ring space. The calculation
can be sped up by using reciprocal divide which is multiplication.

Since ring_size can only be configured by module parameter, so it doesn't
have to be passed around everywhere. Also it should be unsigned
since it is number of pages.

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

drivers/net/hyperv/netvsc.c

@@ -31,6 +31,7 @@
 #include <linux/vmalloc.h>
 #include <linux/rtnetlink.h>
 #include <linux/prefetch.h>
+#include <linux/reciprocal_div.h>
 
 #include <asm/sync_bitops.h>
 
@@ -588,14 +589,11 @@ void netvsc_device_remove(struct hv_device *device)
  * Get the percentage of available bytes to write in the ring.
  * The return value is in range from 0 to 100.
  */
-static inline u32 hv_ringbuf_avail_percent(
-		struct hv_ring_buffer_info *ring_info)
+static u32 hv_ringbuf_avail_percent(const struct hv_ring_buffer_info *ring_info)
 {
-	u32 avail_read, avail_write;
+	u32 avail_write = hv_get_bytes_to_write(ring_info);
 
-	hv_get_ringbuffer_availbytes(ring_info, &avail_read, &avail_write);
-
-	return avail_write * 100 / ring_info->ring_datasize;
+	return reciprocal_divide(avail_write  * 100, netvsc_ring_reciprocal);
 }
 
 static inline void netvsc_free_send_slot(struct netvsc_device *net_device,
@@ -1249,7 +1247,6 @@ struct netvsc_device *netvsc_device_add(struct hv_device *device,
 				const struct netvsc_device_info *device_info)
 {
 	int i, ret = 0;
-	int ring_size = device_info->ring_size;
 	struct netvsc_device *net_device;
 	struct net_device *ndev = hv_get_drvdata(device);
 	struct net_device_context *net_device_ctx = netdev_priv(ndev);
@@ -1261,8 +1258,6 @@ struct netvsc_device *netvsc_device_add(struct hv_device *device,
 	for (i = 0; i < VRSS_SEND_TAB_SIZE; i++)
 		net_device_ctx->tx_table[i] = 0;
 
-	net_device->ring_size = ring_size;
-
 	/* Because the device uses NAPI, all the interrupt batching and
 	 * control is done via Net softirq, not the channel handling
 	 */
@@ -1289,10 +1284,9 @@ struct netvsc_device *netvsc_device_add(struct hv_device *device,
 		       netvsc_poll, NAPI_POLL_WEIGHT);
 
 	/* Open the channel */
-	ret = vmbus_open(device->channel, ring_size * PAGE_SIZE,
-			 ring_size * PAGE_SIZE, NULL, 0,
-			 netvsc_channel_cb,
-			 net_device->chan_table);
+	ret = vmbus_open(device->channel, netvsc_ring_bytes,
+			 netvsc_ring_bytes,  NULL, 0,
+			 netvsc_channel_cb, net_device->chan_table);
 
 	if (ret != 0) {
 		netif_napi_del(&net_device->chan_table[0].napi);