linux-kernel - Re: [PATCH net-next v6 01/10] xsk: align &xdp_buff

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Message-ID: <87wmgfaglm.fsf@toke.dk>
Date: Wed, 04 Dec 2024 11:27:01 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend
 <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Maciej Fijalkowski
 <maciej.fijalkowski@...el.com>, Stanislav Fomichev <sdf@...ichev.me>,
 Magnus Karlsson <magnus.karlsson@...el.com>,
 nex.sw.ncis.osdt.itp.upstreaming@...el.com, bpf@...r.kernel.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 01/10] xsk: align &xdp_buff_xsk harder

Alexander Lobakin <aleksander.lobakin@...el.com> writes:

> After the series "XSk buff on a diet" by Maciej, the greatest pow-2
> which &xdp_buff_xsk can be divided got reduced from 16 to 8 on x86_64.
> Also, sizeof(xdp_buff_xsk) now is 120 bytes, which, taking the previous
> sentence into account, leads to that it leaves 8 bytes at the end of
> cacheline, which means an array of buffs will have its elements
> messed between the cachelines chaotically.
> Use __aligned_largest for this struct. This alignment is usually 16
> bytes, which makes it fill two full cachelines and align an array
> nicely. ___cacheline_aligned may be excessive here, especially on
> arches with 128-256 byte CLs, as well as 32-bit arches (76 -> 96
> bytes on MIPS32R2), while not doing better than _largest.
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>

Ohh, didn't know about that attribute - neat!

Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>