target/linux/generic/pending-3.18/083-solos-pci-Increase-headroom-on-received-packets.patch

   1 From: David Woodhouse <dwmw2@infradead.org>
   2 Date: Thu, 17 Sep 2015 11:19:53 +0100
   3 Subject: [PATCH] solos-pci: Increase headroom on received packets
   4 MIME-Version: 1.0
   5 Content-Type: text/plain; charset=UTF-8
   6 Content-Transfer-Encoding: 8bit
   7
   8 A comment in include/linux/skbuff.h says that:
   9
  10  * Various parts of the networking layer expect at least 32 bytes of
  11  * headroom, you should not reduce this.
  12
  13 This was demonstrated by a panic when handling fragmented IPv6 packets:
  14 http://marc.info/?l=linux-netdev&m=144236093519172&w=2
  15
  16 It's not entirely clear if that comment is still valid — and if it is,
  17 perhaps netif_rx() ought to be enforcing it with a warning.
  18
  19 But either way, it is rather stupid from a performance point of view
  20 for us to be receiving packets into a buffer which doesn't have enough
  21 room to prepend an Ethernet header — it means that *every* incoming
  22 packet is going to be need to be reallocated. So let's fix that.
  23
  24 Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
  25 ---
  26
  27 --- a/drivers/atm/solos-pci.c
  28 +++ b/drivers/atm/solos-pci.c
  29 @@ -805,7 +805,12 @@ static void solos_bh(unsigned long card_
  30                                         continue;
  31                                 }
  32
  33 -                               skb = alloc_skb(size + 1, GFP_ATOMIC);
  34 +                               /* Use netdev_alloc_skb() because it adds NET_SKB_PAD of
  35 +                                * headroom, and ensures we can route packets back out an
  36 +                                * Ethernet interface (for example) without having to
  37 +                                * reallocate. Adding NET_IP_ALIGN also ensures that both
  38 +                                * PPPoATM and PPPoEoBR2684 packets end up aligned. */
  39 +                               skb = netdev_alloc_skb_ip_align(NULL, size + 1);
  40                                 if (!skb) {
  41                                         if (net_ratelimit())
  42                                                 dev_warn(&card->dev->dev, "Failed to allocate sk_buff for RX\n");
  43 @@ -869,7 +874,10 @@ static void solos_bh(unsigned long card_
  44                 /* Allocate RX skbs for any ports which need them */
  45                 if (card->using_dma && card->atmdev[port] &&
  46                     !card->rx_skb[port]) {
  47 -                       struct sk_buff *skb = alloc_skb(RX_DMA_SIZE, GFP_ATOMIC);
  48 +                       /* Unlike the MMIO case (qv) we can't add NET_IP_ALIGN
  49 +                        * here; the FPGA can only DMA to addresses which are
  50 +                        * aligned to 4 bytes. */
  51 +                       struct sk_buff *skb = dev_alloc_skb(RX_DMA_SIZE);
  52                         if (skb) {
  53                                 SKB_CB(skb)->dma_addr =
  54                                         pci_map_single(card->dev, skb->data,