pasemi_mac: further performance tweaks

pasemi_mac: further performance tweaks

Misc driver tweaks for pasemi_mac:
	* Increase ring size (really needed mostly on 10G)
	* Take out an unneeded barrier
	* Move around a few prefetches and reorder a few calls
	* Don't try to clean on full tx buffer, just let things
	  take their course and stop the queue directly
	* Avoid filling on the same line as the interface is
	  working on to reduce cache line bouncing
	* Avoid unneeded clearing of software state (and make the
	  interface shutdown code handle it)
	* Fix up some of the tx ring wrap logic.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/net/pasemi_mac.c b/drivers/net/pasemi_mac.c
index b3994f5..4a451f8 100644 (file)
--- a/drivers/net/pasemi_mac.c
+++ b/drivers/net/pasemi_mac.c
@@ -56,8 +56,8 @@
 
 
 /* Must be a power of two */
-#define RX_RING_SIZE 512
-#define TX_RING_SIZE 512
+#define RX_RING_SIZE 4096
+#define TX_RING_SIZE 4096
 
 #define DEFAULT_MSG_ENABLE       \
        (NETIF_MSG_DRV          | \
@@ -336,8 +336,16 @@ static void pasemi_mac_free_tx_resources(struct net_device *dev)
        struct pasemi_mac_buffer *info;
        dma_addr_t dmas[MAX_SKB_FRAGS+1];
        int freed;
+       int start, limit;
 
-       for (i = 0; i < TX_RING_SIZE; i += freed) {
+       start = mac->tx->next_to_clean;
+       limit = mac->tx->next_to_fill;
+
+       /* Compensate for when fill has wrapped and clean has not */
+       if (start > limit)
+               limit += TX_RING_SIZE;
+
+       for (i = start; i < limit; i += freed) {
                info = &TX_RING_INFO(mac, i+1);
                if (info->dma && info->skb) {
                        for (j = 0; j <= skb_shinfo(info->skb)->nr_frags; j++)
@@ -520,9 +528,6 @@ static int pasemi_mac_clean_rx(struct pasemi_mac *mac, int limit)
        n = mac->rx->next_to_clean;
 
        for (count = limit; count; count--) {
-
-               rmb();
-
                macrx = RX_RING(mac, n);
 
                if ((macrx & XCT_MACRX_E) ||
@@ -550,14 +555,10 @@ static int pasemi_mac_clean_rx(struct pasemi_mac *mac, int limit)
                                break;
                }
 
-               prefetchw(info);
-
                skb = info->skb;
-               prefetchw(skb);
-               info->dma = 0;
 
-               pci_unmap_single(mac->dma_pdev, dma, skb->len,
-                                PCI_DMA_FROMDEVICE);
+               prefetch(skb);
+               prefetch(&skb->data_len);
 
                len = (macrx & XCT_MACRX_LLEN_M) >> XCT_MACRX_LLEN_S;
 
@@ -576,10 +577,9 @@ static int pasemi_mac_clean_rx(struct pasemi_mac *mac, int limit)
                } else
                        info->skb = NULL;
 
-               /* Need to zero it out since hardware doesn't, since the
-                * replenish loop uses it to tell when it's done.
-                */
-               RX_BUFF(mac, i) = 0;
+               pci_unmap_single(mac->dma_pdev, dma, len, PCI_DMA_FROMDEVICE);
+
+               info->dma = 0;
 
                skb_put(skb, len);
 
@@ -599,6 +599,11 @@ static int pasemi_mac_clean_rx(struct pasemi_mac *mac, int limit)
                RX_RING(mac, n) = 0;
                RX_RING(mac, n+1) = 0;
 
+               /* Need to zero it out since hardware doesn't, since the
+                * replenish loop uses it to tell when it's done.
+                */
+               RX_BUFF(mac, i) = 0;
+
                n += 2;
        }
 
@@ -621,27 +626,33 @@ static int pasemi_mac_clean_rx(struct pasemi_mac *mac, int limit)
 static int pasemi_mac_clean_tx(struct pasemi_mac *mac)
 {
        int i, j;
-       struct pasemi_mac_buffer *info;
-       unsigned int start, descr_count, buf_count, limit;
+       unsigned int start, descr_count, buf_count, batch_limit;
+       unsigned int ring_limit;
        unsigned int total_count;
        unsigned long flags;
        struct sk_buff *skbs[TX_CLEAN_BATCHSIZE];
        dma_addr_t dmas[TX_CLEAN_BATCHSIZE][MAX_SKB_FRAGS+1];
 
        total_count = 0;
-       limit = TX_CLEAN_BATCHSIZE;
+       batch_limit = TX_CLEAN_BATCHSIZE;
 restart:
        spin_lock_irqsave(&mac->tx->lock, flags);
 
        start = mac->tx->next_to_clean;
+       ring_limit = mac->tx->next_to_fill;
+
+       /* Compensate for when fill has wrapped but clean has not */
+       if (start > ring_limit)
+               ring_limit += TX_RING_SIZE;
 
        buf_count = 0;
        descr_count = 0;
 
        for (i = start;
-            descr_count < limit && i < mac->tx->next_to_fill;
+            descr_count < batch_limit && i < ring_limit;
             i += buf_count) {
                u64 mactx = TX_RING(mac, i);
+               struct sk_buff *skb;
 
                if ((mactx  & XCT_MACTX_E) ||
                    (*mac->tx_status & PAS_STATUS_ERROR))
@@ -651,19 +662,15 @@ restart:
                        /* Not yet transmitted */
                        break;
 
-               info = &TX_RING_INFO(mac, i+1);
-               skbs[descr_count] = info->skb;
+               skb = TX_RING_INFO(mac, i+1).skb;
+               skbs[descr_count] = skb;
 
-               buf_count = 2 + skb_shinfo(info->skb)->nr_frags;
-               for (j = 0; j <= skb_shinfo(info->skb)->nr_frags; j++)
+               buf_count = 2 + skb_shinfo(skb)->nr_frags;
+               for (j = 0; j <= skb_shinfo(skb)->nr_frags; j++)
                        dmas[descr_count][j] = TX_RING_INFO(mac, i+1+j).dma;
 
-
-               info->dma = 0;
                TX_RING(mac, i) = 0;
                TX_RING(mac, i+1) = 0;
-               TX_RING_INFO(mac, i+1).skb = 0;
-               TX_RING_INFO(mac, i+1).dma = 0;
 
                /* Since we always fill with an even number of entries, make
                 * sure we skip any unused one at the end as well.
@@ -672,7 +679,7 @@ restart:
                        buf_count++;
                descr_count++;
        }
-       mac->tx->next_to_clean = i;
+       mac->tx->next_to_clean = i & (TX_RING_SIZE-1);
 
        spin_unlock_irqrestore(&mac->tx->lock, flags);
        netif_wake_queue(mac->netdev);
@@ -683,7 +690,7 @@ restart:
        total_count += descr_count;
 
        /* If the batch was full, try to clean more */
-       if (descr_count == limit)
+       if (descr_count == batch_limit)
                goto restart;
 
        return total_count;
@@ -1106,19 +1113,14 @@ static int pasemi_mac_start_tx(struct sk_buff *skb, struct net_device *dev)
 
        spin_lock_irqsave(&txring->lock, flags);
 
-       if (RING_AVAIL(txring) <= nfrags+3) {
-               spin_unlock_irqrestore(&txring->lock, flags);
-               pasemi_mac_clean_tx(mac);
-               pasemi_mac_restart_tx_intr(mac);
-               spin_lock_irqsave(&txring->lock, flags);
-
-               if (RING_AVAIL(txring) <= nfrags+3) {
-                       /* Still no room -- stop the queue and wait for tx
-                        * intr when there's room.
-                        */
-                       netif_stop_queue(dev);
-                       goto out_err;
-               }
+       /* Avoid stepping on the same cache line that the DMA controller
+        * is currently about to send, so leave at least 8 words available.
+        * Total free space needed is mactx + fragments + 8
+        */
+       if (RING_AVAIL(txring) < nfrags + 10) {
+               /* no room -- stop the queue and wait for tx intr */
+               netif_stop_queue(dev);
+               goto out_err;
        }
 
        TX_RING(mac, txring->next_to_fill) = mactx;
@@ -1137,8 +1139,8 @@ static int pasemi_mac_start_tx(struct sk_buff *skb, struct net_device *dev)
        if (nfrags & 1)
                nfrags++;
 
-       txring->next_to_fill += nfrags + 1;
-
+       txring->next_to_fill = (txring->next_to_fill + nfrags + 1) &
+                               (TX_RING_SIZE-1);
 
        dev->stats.tx_packets++;
        dev->stats.tx_bytes += skb->len;