Messages in this thread | | | Date | Mon, 24 Feb 2014 14:50:28 -0600 | From | Andy Gross <> | 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 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.
> One of the things I am thinking about is the repeated (spin) locking/unlocking > of the virt_dma_chan->lock or vc->lock. In many cases, there's only 1 user or > thread requiring to do a DMA, so I feel the locking is unnecessary and potential > overhead. If there's a sane way to detect this an avoid locking altogether, that > would be great.
I'd expect the locking to not be the source of the problem, especially with your use case.
[snip]
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