[PATCH 2/2] ath10k: do not use coherent memory for tx buffers

Felix Fietkau nbd at openwrt.org
Mon Nov 23 10:34:53 PST 2015

On 2015-11-23 19:25, Peter Oh wrote:
> On 11/23/2015 10:02 AM, Sebastian Gottschall wrote:
>> Am 23.11.2015 um 18:25 schrieb Peter Oh:
>>> Hi,
>>> Have you measured the peak throughput?
>>> The pre-allocated coherent memory concept was introduced as once of 
>>> peak throughput improvement.
>>> IIRC, dma_map_single takes about 4 us on Cortex A7 and 
>>> dma_unmap_single also takes time to invalid cache.
>>> Please share your tput number before and after, so I don't need to 
>>> worry about performance degrade.
>> yes. and this concept fucks up the qualcom ipq806x platform (which has 
>> by default 2 QCA99XX cards). it does not work, since the preallocated 
>> concept allocates too much memory
> Can you specify the number that you're seeing?
> The tx buffer descriptor uses 56KB, so it would require 64KB x 2 slab 
> for 2 cards which is 128KB.
> Are you saying your system does not work because of this 128KB usage?
The reason might be the GFP_DMA flag, which is unnecessary.

- Felix

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