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@@ -0,0 +1,67 @@
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+[RFC] rt2x00: For drivers that only need L2 padding don't realign frames
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+
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+Signed-off-by: Helmut Schaa <helmut.schaa@...>
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+---
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+
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+Ivo, Gertjan, do you remeber by any chance why this alignment stuff was added
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+in the first place? Was it because of DMA restrictions?
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+
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+While doing some profiling on the rt3052 SoC I noticed that 30-40% time was
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+spent in memmove calls. And the culprit is the memmove aligning the payload
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+to a 4byte boundary since that has to move a whole bunch of data.
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+
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+Interesstingly the legacy drivers insert an l2pad between the header and the
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+payload but doesn't realign the payload itself to a 4-byte boundary. Hence,
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+I came up with this patch and indeed CPU usage improves impressively.
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+
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+Only tested on rt2800pci!
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+
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+Thanks,
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+Helmut
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+
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+ drivers/net/wireless/rt2x00/rt2x00queue.c | 30 +++-------------------------
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+ 1 files changed, 4 insertions(+), 26 deletions(-)
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+
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+--- a/drivers/net/wireless/rt2x00/rt2x00queue.c
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++++ b/drivers/net/wireless/rt2x00/rt2x00queue.c
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+@@ -151,36 +151,14 @@ void rt2x00queue_align_frame(struct sk_b
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+ void rt2x00queue_insert_l2pad(struct sk_buff *skb, unsigned int header_length)
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+ {
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+ unsigned int payload_length = skb->len - header_length;
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+- unsigned int header_align = ALIGN_SIZE(skb, 0);
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+- unsigned int payload_align = ALIGN_SIZE(skb, header_length);
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+ unsigned int l2pad = payload_length ? L2PAD_SIZE(header_length) : 0;
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+
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+- /*
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+- * Adjust the header alignment if the payload needs to be moved more
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+- * than the header.
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+- */
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+- if (payload_align > header_align)
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+- header_align += 4;
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+-
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+- /* There is nothing to do if no alignment is needed */
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+- if (!header_align)
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++ if (!l2pad)
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+ return;
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+
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+- /* Reserve the amount of space needed in front of the frame */
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+- skb_push(skb, header_align);
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+-
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+- /*
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+- * Move the header.
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+- */
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+- memmove(skb->data, skb->data + header_align, header_length);
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+-
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+- /* Move the payload, if present and if required */
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+- if (payload_length && payload_align)
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+- memmove(skb->data + header_length + l2pad,
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+- skb->data + header_length + l2pad + payload_align,
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+- payload_length);
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+-
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+- /* Trim the skb to the correct size */
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++ /* insert l2pad -> Move header */
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++ skb_push(skb, l2pad);
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++ memmove(skb->data, skb->data + l2pad, header_length);
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+ skb_trim(skb, header_length + l2pad + payload_length);
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+ }
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+
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Felix Fietkau