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    SubjectRe: Ideas/suggestions to avoid repeated locking and reducing too many lists with dmaengine?
    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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