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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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