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Date: Tue, 03 Nov 2009 09:40:04 +0100
From: Micha Nelissen <micha@neli.hopto.org>
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To: hank peng <pengxihan@gmail.com>,  linuxppc-dev@ozlabs.org
Subject: Re: mpc8548 does not make use of DMA when doing memory copy?
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hank peng wrote:
> I remember normal memory copy can also be done (chosen by user) by DMA
> engine on IOP80331(Intel embedded cpu, xscale arch), so why ppc
> platform didn't make use of DMA doing memory copy, I think it can
> increase performance, please correct me if I am wrong!

AFAIK the DMA engine has only an asynchronous mode (not very smart 
IMHO). This means you always have the overhead of context switch + 
interrupt + context switch, so the transfer has to be quite large for 
this to pay off.

Micha