| 1 | [RFC] rt2x00: For drivers that only need L2 padding don't realign frames |
| 2 | |
| 3 | Signed-off-by: Helmut Schaa <helmut.schaa@...> |
| 4 | --- |
| 5 | |
| 6 | Ivo, Gertjan, do you remeber by any chance why this alignment stuff was added |
| 7 | in the first place? Was it because of DMA restrictions? |
| 8 | |
| 9 | While doing some profiling on the rt3052 SoC I noticed that 30-40% time was |
| 10 | spent in memmove calls. And the culprit is the memmove aligning the payload |
| 11 | to a 4byte boundary since that has to move a whole bunch of data. |
| 12 | |
| 13 | Interesstingly the legacy drivers insert an l2pad between the header and the |
| 14 | payload but doesn't realign the payload itself to a 4-byte boundary. Hence, |
| 15 | I came up with this patch and indeed CPU usage improves impressively. |
| 16 | |
| 17 | Only tested on rt2800pci! |
| 18 | |
| 19 | Thanks, |
| 20 | Helmut |
| 21 | |
| 22 | drivers/net/wireless/rt2x00/rt2x00queue.c | 30 +++------------------------- |
| 23 | 1 files changed, 4 insertions(+), 26 deletions(-) |
| 24 | |
| 25 | --- a/drivers/net/wireless/rt2x00/rt2x00queue.c |
| 26 | +++ b/drivers/net/wireless/rt2x00/rt2x00queue.c |
| 27 | @@ -151,36 +151,14 @@ void rt2x00queue_align_frame(struct sk_b |
| 28 | void rt2x00queue_insert_l2pad(struct sk_buff *skb, unsigned int header_length) |
| 29 | { |
| 30 | unsigned int payload_length = skb->len - header_length; |
| 31 | - unsigned int header_align = ALIGN_SIZE(skb, 0); |
| 32 | - unsigned int payload_align = ALIGN_SIZE(skb, header_length); |
| 33 | unsigned int l2pad = payload_length ? L2PAD_SIZE(header_length) : 0; |
| 34 | |
| 35 | - /* |
| 36 | - * Adjust the header alignment if the payload needs to be moved more |
| 37 | - * than the header. |
| 38 | - */ |
| 39 | - if (payload_align > header_align) |
| 40 | - header_align += 4; |
| 41 | - |
| 42 | - /* There is nothing to do if no alignment is needed */ |
| 43 | - if (!header_align) |
| 44 | + if (!l2pad) |
| 45 | return; |
| 46 | |
| 47 | - /* Reserve the amount of space needed in front of the frame */ |
| 48 | - skb_push(skb, header_align); |
| 49 | - |
| 50 | - /* |
| 51 | - * Move the header. |
| 52 | - */ |
| 53 | - memmove(skb->data, skb->data + header_align, header_length); |
| 54 | - |
| 55 | - /* Move the payload, if present and if required */ |
| 56 | - if (payload_length && payload_align) |
| 57 | - memmove(skb->data + header_length + l2pad, |
| 58 | - skb->data + header_length + l2pad + payload_align, |
| 59 | - payload_length); |
| 60 | - |
| 61 | - /* Trim the skb to the correct size */ |
| 62 | + /* insert l2pad -> Move header */ |
| 63 | + skb_push(skb, l2pad); |
| 64 | + memmove(skb->data, skb->data + l2pad, header_length); |
| 65 | skb_trim(skb, header_length + l2pad + payload_length); |
| 66 | } |
| 67 | |
| 68 | |
