asix: asix_rx_fixup surgery to reduce skb truesizes

asix_rx_fixup() is complex, and does some unnecessary memory copies (at
least on x86 where NET_IP_ALIGN is 0)

Also, it tends to provide skbs with a big truesize (4096+256 with
MTU=1500) to upper stack, so incoming trafic consume a lot of memory and
I noticed early packet drops because we hit socket rcvbuf too fast.

Switch to a different strategy, using copybreak so that we provide nice
skbs to upper stack (including the NET_SKB_PAD to avoid future head
reallocations in some paths)

With this patch, I no longer see packets drops or tcp collapses on
various tcp workload with a AX88772 adapter.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Aurelien Jacobs <aurel@gnuage.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Trond Wuellner <trond@chromium.org>
Cc: Grant Grundler <grundler@chromium.org>
Cc: Paul Stewart <pstew@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 68 deletions

diff --git a/drivers/net/usb/asix.c b/drivers/net/usb/asix.c
index 8e84f5bdd6ca..25fe1838d886 100644
--- a/drivers/net/usb/asix.c
+++ b/drivers/net/usb/asix.c
@@ -305,88 +305,40 @@ asix_write_cmd_async(struct usbnet *dev, u8 cmd, u16 value, u16 index,
 
 static int asix_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 {
-        u8  *head;
-        u32  header;
-        char *packet;
-        struct sk_buff *ax_skb;
-        u16 size;
+        int offset = 0;
 
-        head = (u8 *) skb->data;
-        memcpy(&header, head, sizeof(header));
-        le32_to_cpus(&header);
-        packet = head + sizeof(header);
+        while (offset + sizeof(u32) < skb->len) {
+                struct sk_buff *ax_skb;
+                u16 size;
+                u32 header = get_unaligned_le32(skb->data + offset);
 
-        skb_pull(skb, 4);
-
-        while (skb->len > 0) {
-                if ((header & 0x07ff) != ((~header >> 16) & 0x07ff))
-                        netdev_err(dev->net, "asix_rx_fixup() Bad Header Length\n");
+                offset += sizeof(u32);
 
                 /* get the packet length */
-                size = (u16) (header & 0x000007ff);
-
-                if ((skb->len) - ((size + 1) & 0xfffe) == 0) {
-                        u8 alignment = (unsigned long)skb->data & 0x3;
-                        if (alignment != 0x2) {
-                                /*
-                                 * not 16bit aligned so use the room provided by
-                                 * the 32 bit header to align the data
-                                 *
-                                 * note we want 16bit alignment as MAC header is
-                                 * 14bytes thus ip header will be aligned on
-                                 * 32bit boundary so accessing ipheader elements
-                                 * using a cast to struct ip header wont cause
-                                 * an unaligned accesses.
-                                 */
-                                u8 realignment = (alignment + 2) & 0x3;
-                                memmove(skb->data - realignment,
-                                        skb->data,
-                                        size);
-                                skb->data -= realignment;
-                                skb_set_tail_pointer(skb, size);
-                        }
-                        return 2;
+                size = (u16) (header & 0x7ff);
+                if (size != ((~header >> 16) & 0x07ff)) {
+                        netdev_err(dev->net, "asix_rx_fixup() Bad Header Length\n");
+                        return 0;
                 }
 
-                if (size > dev->net->mtu + ETH_HLEN) {
+                if ((size > dev->net->mtu + ETH_HLEN) ||
+                    (size + offset > skb->len)) {
                         netdev_err(dev->net, "asix_rx_fixup() Bad RX Length %d\n",
                                    size);
                         return 0;
                 }
-                ax_skb = skb_clone(skb, GFP_ATOMIC);
-                if (ax_skb) {
-                        u8 alignment = (unsigned long)packet & 0x3;
-                        ax_skb->len = size;
-
-                        if (alignment != 0x2) {
-                                /*
-                                 * not 16bit aligned use the room provided by
-                                 * the 32 bit header to align the data
-                                 */
-                                u8 realignment = (alignment + 2) & 0x3;
-                                memmove(packet - realignment, packet, size);
-                                packet -= realignment;
-                        }
-                        ax_skb->data = packet;
-                        skb_set_tail_pointer(ax_skb, size);
-                        usbnet_skb_return(dev, ax_skb);
-                } else {
+                ax_skb = netdev_alloc_skb_ip_align(dev->net, size);
+                if (!ax_skb)
                         return 0;
-                }
-
-                skb_pull(skb, (size + 1) & 0xfffe);
 
-                if (skb->len < sizeof(header))
-                        break;
+                skb_put(ax_skb, size);
+                memcpy(ax_skb->data, skb->data + offset, size);
+                usbnet_skb_return(dev, ax_skb);
 
-                head = (u8 *) skb->data;
-                memcpy(&header, head, sizeof(header));
-                le32_to_cpus(&header);
-                packet = head + sizeof(header);
-                skb_pull(skb, 4);
+                offset += (size + 1) & 0xfffe;
         }
 
-        if (skb->len < 0) {
+        if (skb->len != offset) {
                 netdev_err(dev->net, "asix_rx_fixup() Bad SKB Length %d\n",
                            skb->len);
                 return 0;
@@ -1541,7 +1493,7 @@ static const struct driver_info ax88772_info = {
         .status = asix_status,
         .link_reset = ax88772_link_reset,
         .reset = ax88772_reset,
-        .flags = FLAG_ETHER | FLAG_FRAMING_AX | FLAG_LINK_INTR,
+        .flags = FLAG_ETHER | FLAG_FRAMING_AX | FLAG_LINK_INTR | FLAG_MULTI_PACKET,
         .rx_fixup = asix_rx_fixup,
         .tx_fixup = asix_tx_fixup,
 };