On Thu, 2012-09-06 at 10:50 +0200, Oliver Neukum wrote: > On Thursday 06 September 2012 10:13:01 Alexey ORISHKO wrote: > > Rx path: > > 4. IP packets are cloned to separate skb and length of actual data > set to eth packet size, while skb size is still the same as skb > containing full NTB frame. This causes problems with TCP stack when > throughput is high because of flow control in the stack, if too much > data allocated. > > Someone suggested a patch for it, which was rejected. Anyway, I > don't think copy data to a new skb would be a nice solution, but > keeping several clones with size equal to incoming skb in not good > either. > > Perhaps the problem is using an skb for aggregate reception at all. > Possibly enough buffers of fixed size should be allocated on open and > reused, > not freed. Really skb_clone() use should be removed from cdc_ncm_rx_fixup() Unless you expect 10Gbit speed from this driver, skb_clone() is the worst possible strategy. Allocating fresh skbs of the right size permits better memory use and allows TCP coalescing as well. The use of skb_clone() forces some parts of the stack to perform a full copy anyway. It's still unclear to me with we use up to 32KB blocks in USB drivers... -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
