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

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Date:	Thu, 25 Aug 2011 20:52:39 -0700
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Dean Nelson <dnelson@...hat.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH net-next-2.6] e1000: save skb counts in TX to avoid
 cache misses

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@...gle.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@...hat.com> 

Acked-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

Looks fine.

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