netdev - Re: intermittant petabyte usage reported with broadcom nic

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Date:	13 Apr 2007 03:15:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Roland Dreier <rdreier@...co.com>
Cc:	CaT <cat@....com.au>, Michael Chan <mchan@...adcom.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: intermittant petabyte usage reported with broadcom nic

Roland Dreier <rdreier@...co.com> writes:

> [Adding Michael Chan, who seems to look after bnx2, to the cc list]
> 
>  > To clarify it's an Intel Dual Core Xeon (I just wound up as thinking of
>  > them all as amd64s). Network card driver in use is the one defined by
>  > CONFIG_BNX2. Kernel's monolithic.
> 
> From a quick look at bnx2.c, it seems that the driver gives the NIC
> (firmware?) a block of memory to DMA stats into, and just reads from
> that memory in its get_stats method.  So if you're seeing wonky stats
> from the NIC intermittently, my best guess would be that firmware is
> occasionally writing junk into the stats block.

When only the firmware is writing to that area it could be put
into an own page and then write protected with change_page_attr()
That would catch any corruption coming from the rest of the kernel.

-Andi
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