On 11/08/13 16:08, Rafał Miłecki wrote:
2013/8/9 Florian Fainelli <f.faine...@gmail.com>:
I am looking at bgmac_dma_rx_read() and I do not quite understand why
you would need to copy data to the newly allocated SKB as it might
really be killing performance here. Looking at b44, the code path
doing this is just when the packet is smaller (say less than 256
bytes) because in that case, the cost of a data cache invalidate might
be higher than a fresh allocation plus memcpy(). Rather, the logic I
would use is the following:
- consume a packet from the DMA RX ring at a given index
- dma_sync_single_for_cpu() this packet
- call netif_receive_skb() for this packet
- allocate a new SKB for the same RX ring index
Eventually if you realize that for small packets you had better do a
new allocation plus memcpy() (aka: copybreak) you could try that.
I've implemented that solution, but it didn't really help much :(
Well, http://patchwork.ozlabs.org/patch/220961/ seems to suggest that
bgmac can produce unaligned accesses, so I assume the memcpy() is used
to avoid that. You could try removing the new allocation and memcpy(),
add in the IP stack unaligned access patches from ar71xx and see if that
helps...
--
Robert Bradley
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