e1000: save skb counts in TX to avoid cache misses

dnlsn · davem330 · commit 31c15a2f24eb · 2011-08-26T12:55:18.000-04:00
Virtual Machines with emulated e1000 network adapter running on Parallels' server were seeing kernel panics due to the e1000 driver dereferencing an unexpected NULL pointer retrieved from buffer_info->skb. The problem has been addressed for the e1000e driver, but not for the e1000. Since the two drivers share similar code in the affected area, a port of the following e1000e driver commit solves the issue for the e1000 driver: commit 9ed318d Author: Tom Herbert <therbert@google.com> Date: Wed May 5 14:02:27 2010 +0000 e1000e: save skb counts in TX to avoid cache misses In e1000_tx_map, precompute number of segements and bytecounts which are derived from fields in skb; these are stored in buffer_info. When cleaning tx in e1000_clean_tx_irq use the values in the associated buffer_info for statistics counting, this eliminates cache misses on skb fields. Signed-off-by: Dean Nelson <dnelson@redhat.com> Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/intel/e1000/e1000.h b/drivers/net/ethernet/intel/e1000/e1000.h
@@ -150,6 +150,8 @@ struct e1000_buffer {
 	unsigned long time_stamp;
 	u16 length;
 	u16 next_to_watch;
+	unsigned int segs;
+	unsigned int bytecount;
 	u16 mapped_as_page;
 };
 
diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -2848,7 +2848,7 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
 	struct e1000_buffer *buffer_info;
 	unsigned int len = skb_headlen(skb);
 	unsigned int offset = 0, size, count = 0, i;
-	unsigned int f;
+	unsigned int f, bytecount, segs;
 
 	i = tx_ring->next_to_use;
 
@@ -2949,7 +2949,13 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
 		}
 	}
 
+	segs = skb_shinfo(skb)->gso_segs ?: 1;
+	/* multiply data chunks by size of headers */
+	bytecount = ((segs - 1) * skb_headlen(skb)) + skb->len;
+
 	tx_ring->buffer_info[i].skb = skb;
+	tx_ring->buffer_info[i].segs = segs;
+	tx_ring->buffer_info[i].bytecount = bytecount;
 	tx_ring->buffer_info[first].next_to_watch = i;
 
 	return count;
@@ -3623,14 +3629,8 @@ static bool e1000_clean_tx_irq(struct e1000_adapter *adapter,
 			cleaned = (i == eop);
 
 			if (cleaned) {
-				struct sk_buff *skb = buffer_info->skb;
-				unsigned int segs, bytecount;
-				segs = skb_shinfo(skb)->gso_segs ?: 1;
-				/* multiply data chunks by size of headers */
-				bytecount = ((segs - 1) * skb_headlen(skb)) +
-				            skb->len;
-				total_tx_packets += segs;
-				total_tx_bytes += bytecount;
+				total_tx_packets += buffer_info->segs;
+				total_tx_bytes += buffer_info->bytecount;
 			}
 			e1000_unmap_and_free_tx_resource(adapter, buffer_info);
 			tx_desc->upper.data = 0;
