Re: application needs fast access to physical memory

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Nov 18, 2010 at 11:24:22PM +1100, Michael Ellerman wrote:
> On Wed, 2010-11-17 at 16:03 -0600, steven.lin@teradyne.com wrote:
> > My application needs a fast way to access a specific physical DDR
> > memory region. The application runs on an MPC8548 PowerPC which has an
> > MMU. I've tried two approaches that are typical for Linux, mmap() and
> > using a kernel module that implements read()/write() into this region
> > and I'm finding that performance is very slow for both. It's a couple
> > orders of magnitude slower than, for example, copying a large buffer
> > from one place in the application's virtual memory to another place in
> > the application's virtual memory.
> 
> The mmap() version should basically run at "full speed", at least once
> you've faulted the address range in.
> 
> This specific DDR region isn't specifically slow is it ? :)

The other theory that springs to mind is whatever method you're using
to access the region enabling cacheing?

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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