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Subject: Re: Discussion about iopa()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Dan Malek <dan@embeddedalley.com>
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Date: Sat, 10 Feb 2007 13:37:01 +1100
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Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>,
	Timur Tabi <timur@freescale.com>
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On Fri, 2007-02-09 at 12:08 -0500, Dan Malek wrote:
> On Feb 8, 2007, at 8:41 AM, Timur Tabi wrote:
> 
> > Walking the page table is slower than using pointer math, so you  
> > want to
> > avoid iopa() if you can.
> 
> Big deal.  With all of the other kernel bloat
> going on you want to argue about a couple
> of memory accesses?  :-)

We are fairly careful about not bloating fast path in general. It's more
than a couple of memory accesses, especially with PTEs in highmem where
it involves kmap.

Ben.