From: Sergei Shtylyov > Sent: 24 April 2015 19:27 ... > > If you have ethernet hardware that requires tx or rx buffers to be on > > 4n boundaries you should send it back as 'not fit for purpose'. > > The RX buffers can be adjusted with skb_resrerve(), it's only the TX > buffers that need to be copied... If the processor can't perform misaligned reads (don't know what is on your SoC, but I suspect it can't - crossing page boundaries is hard) then the rx buffer will have to be re-aligned in software. Even the 'userdata' part will typically end up with an expensive misaligned buffer copy. Even on x86 the misaligned transfers are probably measurable. > I'm afraid we can't. :-) > However, my colleague has suggested a scheme minimizing the copying: > only up to 3 first bytes need to be copied to the driver's internal buffers, > the rest can be sent from an skb itself. That would require substantial > changes to the driver though... There might be a restriction on the length of buffer fragments. You might be able to alternate 14 and 1500+ byte receive buffers. The frame following a slightly overlong one would be 'wrong'. David -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
