netdev - Re: [PATCH net] eth: fbnic: don't build the driver when skb has more than 25 frags

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Message-ID: <498dac82-3fbe-4490-a322-bb7420370d0b@redhat.com>
Date: Wed, 17 Jul 2024 16:50:54 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 alexanderduyck@...com, kernel-team@...a.com
Subject: Re: [PATCH net] eth: fbnic: don't build the driver when skb has more
 than 25 frags



On 7/17/24 16:12, Jakub Kicinski wrote:
> On Wed, 17 Jul 2024 15:44:09 +0200 Paolo Abeni wrote:
>> I think that with aarch MAX_SKB_FRAGS should be max 21. Aarch cacheline
>> size is 128, right? The frag independent part of skb_shared_info takes
>> 48 bytes, and sizeof(skb_frag_t) == 16:
>>
>> (512 - 128 - 48)/16 = 21
> 
> Hm, my grep foo must be low, I don't see aarch64 with 128B cache lines.
> But I do see powerpc, so we can stick to 21 to be safe.

Yup, it looks like I was wrong with aarch64, but there are indeed other 
64bits arches with 128 bytes cache line size.

Given this impact builds, I think we are better off with a fast repost 
(before the 24h grace period).

Thanks,

Paolo