[RFC] rt2x00: For drivers that only need L2 padding don't realign frames Signed-off-by: Helmut Schaa --- Ivo, Gertjan, do you remeber by any chance why this alignment stuff was added in the first place? Was it because of DMA restrictions? While doing some profiling on the rt3052 SoC I noticed that 30-40% time was spent in memmove calls. And the culprit is the memmove aligning the payload to a 4byte boundary since that has to move a whole bunch of data. Interesstingly the legacy drivers insert an l2pad between the header and the payload but doesn't realign the payload itself to a 4-byte boundary. Hence, I came up with this patch and indeed CPU usage improves impressively. Only tested on rt2800pci! Thanks, Helmut drivers/net/wireless/rt2x00/rt2x00queue.c | 30 +++------------------------- 1 files changed, 4 insertions(+), 26 deletions(-) --- a/drivers/net/wireless/rt2x00/rt2x00queue.c +++ b/drivers/net/wireless/rt2x00/rt2x00queue.c @@ -162,36 +162,14 @@ void rt2x00queue_align_frame(struct sk_b void rt2x00queue_insert_l2pad(struct sk_buff *skb, unsigned int header_length) { unsigned int payload_length = skb->len - header_length; - unsigned int header_align = ALIGN_SIZE(skb, 0); - unsigned int payload_align = ALIGN_SIZE(skb, header_length); unsigned int l2pad = payload_length ? L2PAD_SIZE(header_length) : 0; - /* - * Adjust the header alignment if the payload needs to be moved more - * than the header. - */ - if (payload_align > header_align) - header_align += 4; - - /* There is nothing to do if no alignment is needed */ - if (!header_align) + if (!l2pad) return; - /* Reserve the amount of space needed in front of the frame */ - skb_push(skb, header_align); - - /* - * Move the header. - */ - memmove(skb->data, skb->data + header_align, header_length); - - /* Move the payload, if present and if required */ - if (payload_length && payload_align) - memmove(skb->data + header_length + l2pad, - skb->data + header_length + l2pad + payload_align, - payload_length); - - /* Trim the skb to the correct size */ + /* insert l2pad -> Move header */ + skb_push(skb, l2pad); + memmove(skb->data, skb->data + l2pad, header_length); skb_trim(skb, header_length + l2pad + payload_length); }