From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: Software prefetching considered harmful
Date: Sat, 21 May 2011 14:18:55 +1000
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To: Michael Cree <mcree@orcon.net.nz>
Cc: Ingo Molnar <mingo@elte.hu>, Linus Torvalds <torvalds@linux-foundation.org>, linux-arch@vger.kernel.org, David Miller <davem@davemloft.net>, Russell King <rmk@arm.linux.org.uk>

On Sat, 2011-05-21 at 15:37 +1200, Michael Cree wrote:
> While this is not a concern to the kernel (it obviously has access to
> location 0) 

Not that obvious... dunno how you do your memory map on alpha but on
most architectures, 0 is userspace even when you're in the kernel and is
typically not mapped.

Cheers,
Ben.

> I can imagine some neophyte thinking (as I have done myself)
> "I'll look to see how the kernel implements lists and use that because
> it will be both clever and well tested code" without realising that the
> prefetch of a NULL is very inefficient for userspace!
> 
>