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    SubjectRe: [PATCH 2/7] dmaengine: omap-dma: Complete the cookie first on transfer completion
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    On 07/18/16 13:34, Russell King - ARM Linux wrote:
    > On Thu, Jul 14, 2016 at 03:42:37PM +0300, Peter Ujfalusi wrote:
    >> Before looking for the next descriptor to start, complete the just finished
    >> cookie.
    >
    > This change will reduce performance as we no longer have an overlap
    > between the next request starting to be dealt with in the hardware
    > vs the previous request being completed.

    vchan_cookie_complete() will only mark the cookie completed, adds the vd to
    the desc_completed list (it was deleted from desc_issued list when it was
    started by omap_dma_start_desc) and schedule the tasklet to deal with the real
    completion later.
    Marking the just finished descriptor/cookie done first then looking for
    possible descriptors in the queue to start feels like a better sequence.

    After a quick grep in the kernel source: only omap-dma.c was starting the next
    transfer before marking the current completed descriptor/cookie done.

    > Your commit log doesn't
    > say _why_ the change is being made, it merely tells us what the
    > patch is doing, which we can see already.
    >
    > Please describe changes a little better.
    >


    --
    Péter

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