From 95162d652477f6e3d04687f5d39d443fcc64d8d7 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 5 Jul 2012 04:31:01 +0000 Subject: [PATCH] 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 Cc: Greg Kroah-Hartman Cc: Allan Chou Cc: Trond Wuellner Cc: Grant Grundler Cc: Paul Stewart Cc: Ming Lei Tested-by: Ming Lei Signed-off-by: David S. Miller --- drivers/net/usb/asix.c | 28 ++++++++++++++++++++++++---- 1 file 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); -- 2.20.1