netdev - Re: [PATCH net] be2net: Increase skb headroom size to 256 bytes

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Date:   Wed, 21 Dec 2016 13:43:38 +0530
From:   Sriharsha Basavapatna <sriharsha.basavapatna@...adcom.com>
To:     David Miller <davem@...emloft.net>
Cc:     Suresh Kumar Reddy Reddygari <suresh.reddy@...adcom.com>,
        netdev@...r.kernel.org,
        Kalesh Anakkur Purayil <kalesh-anakkur.purayil@...adcom.com>
Subject: Re: [PATCH net] be2net: Increase skb headroom size to 256 bytes

On Wed, Dec 21, 2016 at 1:00 AM, David Miller <davem@...emloft.net> wrote:
>
> From: Suresh Reddy <suresh.reddy@...adcom.com>
> Date: Tue, 20 Dec 2016 10:14:30 -0500
>
> > From: Kalesh A P <kalesh-anakkur.purayil@...adcom.com>
> >
> > The driver currently allocates 128 bytes of skb headroom.
> > This was found to be insufficient with some configurations
> > like Geneve tunnels, which resulted in skb head reallocations.
> >
> > Increase the headroom to 256 bytes to fix this.
> >
> > Signed-off-by: Kalesh A P <kalesh-anakkur.purayil@...adcom.com>
> > Signed-off-by: Suresh Reddy <suresh.reddy@...adcom.com>
>
> Adding 128 bytes of headroom just for geneve seems excessive.
>
> Do you really need to add that much?

Hi David,

With geneve, there's a fixed 8 byte header followed by a variable
options header of max length 256 bytes. And with vlan+ipv6 combination
we could run out of 128 bytes headroom even with just the fixed geveve
header (+ outer and inner eth/ipv6/transport headers).

Thanks,
-Harsha