Messages in this thread | | | Date | Tue, 25 Feb 2014 12:24:24 +0000 | From | Russell King - ARM Linux <> | Subject | Re: Ideas/suggestions to avoid repeated locking and reducing too many lists with dmaengine? |
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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: > > 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.
-- FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly improving, and getting towards what was expected from it.
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