e1000: save skb counts in TX to avoid cache misses
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>
diff --git a/drivers/net/ethernet/intel/e1000/e1000.h b/drivers/net/ethernet/intel/e1000/e1000.h
index 24f41da..4ea87b1 100644
--- a/drivers/net/ethernet/intel/e1000/e1000.h
+++ b/drivers/net/ethernet/intel/e1000/e1000.h
@@ -150,6 +150,8 @@
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
index 7c280e5..4a32c15 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_main.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -2848,7 +2848,7 @@
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 @@
}
}
+ 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 @@
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;