netdev - Re: [PATCH net v2 1/2] gianfar: Replace skb_realloc_headroom with skb_cow

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Message-ID: <19c3385d-7974-b5bd-3d5a-51d3d87919b0@gmail.com>
Date:   Tue, 3 Nov 2020 19:16:29 +0100
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        "james.jurack@...tek.com" <james.jurack@...tek.com>
Subject: Re: [PATCH net v2 1/2] gianfar: Replace skb_realloc_headroom with
 skb_cow_head for PTP



On 11/3/20 6:49 PM, Vladimir Oltean wrote:
> On Tue, Nov 03, 2020 at 05:41:36PM +0000, Claudiu Manoil wrote:
>> This is the patch:
>> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=d145c9031325fed963a887851d9fa42516efd52b
>>
>> are you sure you have it applied?
> 
> Actually? No, I didn't have it applied... I had thought that net had
> been already merged into net-next, for some reason :-/
> Let me run the test for a few more tens of minutes with the patch
> applied.
> 

I find strange that the local TCP traffic can end up calling skb_realloc_headromm() in the old kernels.

Normally TCP reserves a lot of bytes for headers.

#define MAX_TCP_HEADER     L1_CACHE_ALIGN(128 + MAX_HEADER)

It should accommodate the gianfar needs for additional 24 bytes,
even if LL_MAX_HEADER is 32 in your kernel build perhaps.