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/hyperv_net.h

@@ -146,7 +146,6 @@ struct hv_netvsc_packet {
 
 struct netvsc_device_info {
 	unsigned char mac_adr[ETH_ALEN];
-	int  ring_size;
 	u32  num_chn;
 	u32  send_sections;
 	u32  recv_sections;
@@ -188,6 +187,9 @@ struct rndis_message;
 struct netvsc_device;
 struct net_device_context;
 
+extern u32 netvsc_ring_bytes;
+extern struct reciprocal_value netvsc_ring_reciprocal;
+
 struct netvsc_device *netvsc_device_add(struct hv_device *device,
 					const struct netvsc_device_info *info);
 int netvsc_alloc_recv_comp_ring(struct netvsc_device *net_device, u32 q_idx);
@@ -804,8 +806,6 @@ struct netvsc_device {
 
 	struct rndis_device *extension;
 
-	int ring_size;
-
 	u32 max_pkt; /* max number of pkt in one send, e.g. 8 */
 	u32 pkt_align; /* alignment bytes, e.g. 8 */
 

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);

drivers/net/hyperv/netvsc_drv.c

@@ -35,6 +35,7 @@
 #include <linux/slab.h>
 #include <linux/rtnetlink.h>
 #include <linux/netpoll.h>
+#include <linux/reciprocal_div.h>
 
 #include <net/arp.h>
 #include <net/route.h>
@@ -54,9 +55,11 @@
 #define LINKCHANGE_INT (2 * HZ)
 #define VF_TAKEOVER_INT (HZ / 10)
 
-static int ring_size = 128;
-module_param(ring_size, int, S_IRUGO);
+static unsigned int ring_size __ro_after_init = 128;
+module_param(ring_size, uint, S_IRUGO);
 MODULE_PARM_DESC(ring_size, "Ring buffer size (# of pages)");
+unsigned int netvsc_ring_bytes __ro_after_init;
+struct reciprocal_value netvsc_ring_reciprocal __ro_after_init;
 
 static const u32 default_msg = NETIF_MSG_DRV | NETIF_MSG_PROBE |
 				NETIF_MSG_LINK | NETIF_MSG_IFUP |
@@ -860,7 +863,6 @@ static int netvsc_set_channels(struct net_device *net,
 
 	memset(&device_info, 0, sizeof(device_info));
 	device_info.num_chn = count;
-	device_info.ring_size = ring_size;
 	device_info.send_sections = nvdev->send_section_cnt;
 	device_info.send_section_size = nvdev->send_section_size;
 	device_info.recv_sections = nvdev->recv_section_cnt;
@@ -975,7 +977,6 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 		rndis_filter_close(nvdev);
 
 	memset(&device_info, 0, sizeof(device_info));
-	device_info.ring_size = ring_size;
 	device_info.num_chn = nvdev->num_chn;
 	device_info.send_sections = nvdev->send_section_cnt;
 	device_info.send_section_size = nvdev->send_section_size;
@@ -1539,7 +1540,6 @@ static int netvsc_set_ringparam(struct net_device *ndev,
 
 	memset(&device_info, 0, sizeof(device_info));
 	device_info.num_chn = nvdev->num_chn;
-	device_info.ring_size = ring_size;
 	device_info.send_sections = new_tx;
 	device_info.send_section_size = nvdev->send_section_size;
 	device_info.recv_sections = new_rx;
@@ -1995,7 +1995,6 @@ static int netvsc_probe(struct hv_device *dev,
 
 	/* Notify the netvsc driver of the new device */
 	memset(&device_info, 0, sizeof(device_info));
-	device_info.ring_size = ring_size;
 	device_info.num_chn = VRSS_CHANNEL_DEFAULT;
 	device_info.send_sections = NETVSC_DEFAULT_TX;
 	device_info.send_section_size = NETVSC_SEND_SECTION_SIZE;
@@ -2158,11 +2157,13 @@ static int __init netvsc_drv_init(void)
 
 	if (ring_size < RING_SIZE_MIN) {
 		ring_size = RING_SIZE_MIN;
-		pr_info("Increased ring_size to %d (min allowed)\n",
+		pr_info("Increased ring_size to %u (min allowed)\n",
 			ring_size);
 	}
-	ret = vmbus_driver_register(&netvsc_drv);
+	netvsc_ring_bytes = ring_size * PAGE_SIZE;
+	netvsc_ring_reciprocal = reciprocal_value(netvsc_ring_bytes);
 
+	ret = vmbus_driver_register(&netvsc_drv);
 	if (ret)
 		return ret;
 

drivers/net/hyperv/rndis_filter.c

@@ -1040,8 +1040,8 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
 	/* Set the channel before opening.*/
 	nvchan->channel = new_sc;
 
-	ret = vmbus_open(new_sc, nvscdev->ring_size * PAGE_SIZE,
-			 nvscdev->ring_size * PAGE_SIZE, NULL, 0,
+	ret = vmbus_open(new_sc, netvsc_ring_bytes,
+			 netvsc_ring_bytes, NULL, 0,
 			 netvsc_channel_cb, nvchan);
 	if (ret == 0)
 		napi_enable(&nvchan->napi);