Re: [PATCH] solos-pci: Increase headroom on received packets
On Wed, 2015-09-16 at 03:53 -0700, Eric Dumazet wrote: > You should use netdev_alloc_skb() : This helper is better for rx skbs, > as it allows for better packing of frames in GRO or TCP stack. OK, thanks. I don't have a netdev (this is an ATM device) but I can use dev_alloc_skb(). > Also netdev_alloc_skb_ip_align() might handle the NET_IP_ALIGN stuff > for arches that care. I'd briefly considered NET_IP_ALIGN but decided against it because this isn't Ethernet and my hardware header is a nice sane 8 bytes, not 14. But actually, the primary use cases for this are PPPoATM — with 2 bytes of PPP frame type, and PPPoE over BR2684 — with 14 bytes of Ethernet header. So NET_IP_ALIGN would actually make sense. Unfortunately the FPGA can't do DMA to unaligned addresses, so I can't do it in the DMA case. I can do it for the MMIO code path though (which I still haven't tested). I'll send a new patch in a moment... -- dwmw2 smime.p7s Description: S/MIME cryptographic signature
Re: [PATCH] solos-pci: Increase headroom on received packets
On Wed, 2015-09-16 at 11:25 +0100, David Woodhouse wrote: > 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 > --- > Tested in the DMA code path; I don't believe the DMA-capable devices > can still be used in MMIO mode. Simon, Guy, would you be able to test > the MMIO version? You should use netdev_alloc_skb() : This helper is better for rx skbs, as it allows for better packing of frames in GRO or TCP stack. Also netdev_alloc_skb_ip_align() might handle the NET_IP_ALIGN stuff for arches that care. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
