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- [RFC] rt2x00: For drivers that only need L2 padding don't realign frames
- Signed-off-by: Helmut Schaa <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
- @@ -161,36 +161,14 @@ 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);
- }
-
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