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Date: Fri, 24 Oct 2008 11:22:43 +0200
From: "Edgar E. Iglesias" <edgar.iglesias@axis.com>
Subject: Re: [Qemu-devel] [PATCH][RFT] Make DMA timer driven
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To: Paul Brook <paul@codesourcery.com>
Cc: "Edgar E. Iglesias" <edgar@axis.com>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org

On Fri, Oct 24, 2008 at 12:13:49AM +0100, Paul Brook wrote:
> > You can find info regarding CRIS/ETRAX testing here:
> > http://lists.gnu.org/archive/html/qemu-devel/2008-09/msg00279.html
> >
> > I tested the patch. It works but unfortunately DMA transfers to/from
> > the ethernet block now seem to emulate very slowly.
> 
> Is there a reason you're deferring the DMA transfers, rather than completing 
> them immediately? In most cases you want to do the DMA as soon as both ends 
> are ready, and there's no benefit artificially delaying things. Any delay is 
> entirely arbitrary, and won't work reliably.

Hello,

If you are refering to the etrax dma/ethernet, any delays are unintentional. I removed the poll based ethernet receive path, so that rx packets now go straight into the dma without waiting for DMA_run but unfortunately the timer based DMA_run still slows things down for etrax.

I'll try to look at it more when I get a free time slot..

Thanks