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