Messages in this thread | | | Subject | Re: [PATCH 2/7] dmaengine: omap-dma: Complete the cookie first on transfer completion | From | Peter Ujfalusi <> | Date | Tue, 19 Jul 2016 15:35:18 +0300 |
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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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