On Mon, Feb 24, 2014 at 02:50:28PM -0600, Andy Gross wrote:

On Mon, Feb 24, 2014 at 01:03:32PM -0600, Joel Fernandes wrote:

quoted

Hi folks,

Just wanted your thoughts/suggestions on how we can avoid overhead in the EDMA
dmaengine driver. I am seeing a lots of performance drop specially for small
transfers with EDMA versus before raw EDMA was moved to DMAEngine framework
(atleast 25%).

I've seen roughly the same drop in my testing.  In my case it had to do
with the nature of how work is done using virt-dma.  The virt-dma is
predicated on only letting one transaction be active at a time and it
increases the latency for getting the next transaction off.  For large
transactions, it's negligible.  But for small transactions, it is pretty
evident.

Wrong.  virt-dma allows you to fire off the next transaction in the queue
immediately that the previous transaction has finished.  I know this,
because sa11x0-dma does exactly that.

You don't need to wait for the tasklet to be called before starting the
next transaction.

-- 
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improving, and getting towards what was expected from it.