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authorEric Dumazet <edumazet@google.com>2012-07-05 04:31:01 +0000
committerDavid S. Miller <davem@davemloft.net>2012-07-07 16:26:56 -0700
commit95162d652477f6e3d04687f5d39d443fcc64d8d7 (patch)
tree8685d62afd2b8b77fe9d7d866d22733976364bab /drivers/net/usb
parentcabdc8ee3768ceb6367e88c6fe84a66dd667bdf9 (diff)
downloadlinux-95162d652477f6e3d04687f5d39d443fcc64d8d7.tar.bz2
asix: avoid copies in tx path
I noticed excess calls to skb_copy_expand() or memmove() in asix driver. This driver needs to push 4 bytes in front of frame (packet_len) and maybe add 4 bytes after the end (if padlen is 4) So it should set needed_headroom & needed_tailroom to avoid copies. But its not enough, because many packets are cloned before entering asix_tx_fixup() and this driver use skb_cloned() as a lazy way to check if it can push and put additional bytes in frame. Avoid skb_copy_expand() expensive call, using following rules : - We are allowed to push 4 bytes in headroom if skb_header_cloned() is false (and if we have 4 bytes of headroom) - We are allowed to put 4 bytes at tail if skb_cloned() is false (and if we have 4 bytes of tailroom) TCP packets for example are cloned, but skb_header_release() was called in tcp stack, allowing us to use headroom for our needs. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Allan Chou <allan@asix.com.tw> Cc: Trond Wuellner <trond@chromium.org> Cc: Grant Grundler <grundler@chromium.org> Cc: Paul Stewart <pstew@chromium.org> Cc: Ming Lei <tom.leiming@gmail.com> Tested-by: Ming Lei <ming.lei@canonical.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/usb')
-rw-r--r--drivers/net/usb/asix.c28
1 files changed, 24 insertions, 4 deletions
diff --git a/drivers/net/usb/asix.c b/drivers/net/usb/asix.c
index 3ae80eccd0ef..6564c32d3af0 100644
--- a/drivers/net/usb/asix.c
+++ b/drivers/net/usb/asix.c
@@ -358,14 +358,30 @@ static struct sk_buff *asix_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
padlen = ((skb->len + 4) & (dev->maxpacket - 1)) ? 0 : 4;
- if ((!skb_cloned(skb)) &&
- ((headroom + tailroom) >= (4 + padlen))) {
- if ((headroom < 4) || (tailroom < padlen)) {
+ /* We need to push 4 bytes in front of frame (packet_len)
+ * and maybe add 4 bytes after the end (if padlen is 4)
+ *
+ * Avoid skb_copy_expand() expensive call, using following rules :
+ * - We are allowed to push 4 bytes in headroom if skb_header_cloned()
+ * is false (and if we have 4 bytes of headroom)
+ * - We are allowed to put 4 bytes at tail if skb_cloned()
+ * is false (and if we have 4 bytes of tailroom)
+ *
+ * TCP packets for example are cloned, but skb_header_release()
+ * was called in tcp stack, allowing us to use headroom for our needs.
+ */
+ if (!skb_header_cloned(skb) &&
+ !(padlen && skb_cloned(skb)) &&
+ headroom + tailroom >= 4 + padlen) {
+ /* following should not happen, but better be safe */
+ if (headroom < 4 ||
+ tailroom < padlen) {
skb->data = memmove(skb->head + 4, skb->data, skb->len);
skb_set_tail_pointer(skb, skb->len);
}
} else {
struct sk_buff *skb2;
+
skb2 = skb_copy_expand(skb, 4, padlen, flags);
dev_kfree_skb_any(skb);
skb = skb2;
@@ -373,8 +389,8 @@ static struct sk_buff *asix_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
return NULL;
}
+ packet_len = ((skb->len ^ 0x0000ffff) << 16) + skb->len;
skb_push(skb, 4);
- packet_len = (((skb->len - 4) ^ 0x0000ffff) << 16) + (skb->len - 4);
cpu_to_le32s(&packet_len);
skb_copy_to_linear_data(skb, &packet_len, sizeof(packet_len));
@@ -880,6 +896,8 @@ static int ax88172_bind(struct usbnet *dev, struct usb_interface *intf)
dev->net->netdev_ops = &ax88172_netdev_ops;
dev->net->ethtool_ops = &ax88172_ethtool_ops;
+ dev->net->needed_headroom = 4; /* cf asix_tx_fixup() */
+ dev->net->needed_tailroom = 4; /* cf asix_tx_fixup() */
asix_mdio_write(dev->net, dev->mii.phy_id, MII_BMCR, BMCR_RESET);
asix_mdio_write(dev->net, dev->mii.phy_id, MII_ADVERTISE,
@@ -1075,6 +1093,8 @@ static int ax88772_bind(struct usbnet *dev, struct usb_interface *intf)
dev->net->netdev_ops = &ax88772_netdev_ops;
dev->net->ethtool_ops = &ax88772_ethtool_ops;
+ dev->net->needed_headroom = 4; /* cf asix_tx_fixup() */
+ dev->net->needed_tailroom = 4; /* cf asix_tx_fixup() */
embd_phy = ((dev->mii.phy_id & 0x1f) == 0x10 ? 1 : 0);