e1000: save skb counts in TX to avoid cache misses

commit 31c15a2f24ebdab14333d9bf5df49757842ae2ec upstream.

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 9ed318d546a29d7a591dbe648fd1a2efe3be1180
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>
Signed-off-by: Roman Kagan <rkagan@parallels.com>

diff --git a/drivers/net/e1000/e1000.h b/drivers/net/e1000/e1000.h
index 8676899120c301f67eab5de0ffb87b019f18281f..2c71884eb46e9937c4294e39650dfb0d136e97af 100644 (file)
--- a/drivers/net/e1000/e1000.h
+++ b/drivers/net/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/e1000/e1000_main.c b/drivers/net/e1000/e1000_main.c
index 76e8af00d86dab7d79a65842dddadf6cfed337c8..99525f9b41b64623ede0994122804a8a109d83b6 100644 (file)
--- a/drivers/net/e1000/e1000_main.c
+++ b/drivers/net/e1000/e1000_main.c
@@ -2798,7 +2798,7 @@ 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;
 
@@ -2899,7 +2899,13 @@ 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;
@@ -3573,14 +3579,8 @@ 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;