Patchwork [net-next-2.6] e1000: save skb counts in TX to avoid cache misses

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Submitter Dean Nelson
Date Aug. 26, 2011, 12:39 a.m.
Message ID <20110826003923.4083.24862.email-sent-by-dnelson@localhost6.localdomain6>
Download mbox | patch
Permalink /patch/111694/
State Accepted
Delegated to: David Miller
Headers show

Comments

Dean Nelson - Aug. 26, 2011, 12:39 a.m.
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>

---
This patch (backported to RHEL6.2) was verified by Dmitry Skorodumov to solve
Parallels' reported problem.

 drivers/net/ethernet/intel/e1000/e1000.h      |    2 ++
 drivers/net/ethernet/intel/e1000/e1000_main.c |   18 +++++++++---------
 2 files changed, 11 insertions(+), 9 deletions(-)

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Jeff Kirsher - Aug. 26, 2011, 3:52 a.m.
On Thu, 2011-08-25 at 17:39 -0700, Dean Nelson wrote:
> 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>

Looks fine.
David Miller - Aug. 26, 2011, 4:55 p.m.
From: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Date: Thu, 25 Aug 2011 20:52:39 -0700

> On Thu, 2011-08-25 at 17:39 -0700, Dean Nelson wrote:
>> 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>

Applied, thanks.
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Patch

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 @@  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
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 @@  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;