netdev - Re: [PATCH] solos-pci: Increase headroom on received packets

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Date:	Wed, 16 Sep 2015 12:32:03 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, simon@...e.lp0.eu, guy@...verse.com.au,
	linux-atm-general@...ts.sourceforge.net
Subject: 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

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