package/mac80211/patches/606-rt2x00_no_realign.patch

   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