lkml.org 
[lkml]   [2014]   [Feb]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Ideas/suggestions to avoid repeated locking and reducing too many lists with dmaengine?
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]

--
sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
hosted by The Linux Foundation


\
 
 \ /
  Last update: 2014-02-24 22:41    [W:0.545 / U:0.452 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site