netdev - Re: [PATCH net-next 5/6] netfilter: nft_set_pipapo: Store real pointer, adjust later.

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Message-ID: <20250820174401.5addbfc1@elisabeth>
Date: Wed, 20 Aug 2025 17:44:01 +0200
From: Stefano Brivio <sbrivio@...hat.com>
To: Florian Westphal <fw@...len.de>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>
Cc: <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, <netfilter-devel@...r.kernel.org>,
 pablo@...filter.org
Subject: Re: [PATCH net-next 5/6] netfilter: nft_set_pipapo: Store real
 pointer, adjust later.

On Wed, 20 Aug 2025 16:47:37 +0200
Florian Westphal <fw@...len.de> wrote:

> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> The struct nft_pipapo_scratch is allocated, then aligned to the required
> alignment and difference (in bytes) is then saved in align_off. The
> aligned pointer is used later.
> While this works, it gets complicated with all the extra checks if
> all member before map are larger than the required alignment.
> 
> Instead of saving the aligned pointer, just save the returned pointer
> and align the map pointer in nft_pipapo_lookup() before using it. The
> alignment later on shouldn't be that expensive.

The cost of doing the alignment later was the very reason why I added
this whole dance in the first place though. Did you check packet
matching rates before and after this?

-- 
Stefano