netdev - Re: [RFC PATCH 0/2] udp: avoid false sharing on sk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANn89iJGn=GPKF880yctgdxEFi4tgFsX+piGmyLr9MMUuxB0-A@mail.gmail.com>
Date: Mon, 10 Feb 2025 08:49:30 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>, Neal Cardwell <ncardwell@...gle.com>, 
	David Ahern <dsahern@...nel.org>
Subject: Re: [RFC PATCH 0/2] udp: avoid false sharing on sk_tsflags

On Fri, Feb 7, 2025 at 5:24 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> While benchmarking the recently shared page frag revert, I observed a
> lot of cache misses in the UDP RX path due to false sharing between the
> sk_tsflags and the sk_forward_alloc sk fields.
>
> Here comes a solution attempt for such a problem, inspired by commit
> f796feabb9f5 ("udp: add local "peek offset enabled" flag").
>
> The first patch adds a new proto op allowing protocol specific operation
> on tsflags updates, and the 2nd one leverages such operation to cache
> the problematic field in a cache friendly manner.
>
> The need for a new operation is possibly suboptimal, hence the RFC tag,
> but I could not find other good solutions. I considered:
> - moving the sk_tsflags just before 'sk_policy', in the 'sock_read_rxtx'
>   group. It arguably belongs to such group, but the change would create
>   a couple of holes, increasing the 'struct sock' size and would have
>   side effects on other protocols
> - moving the sk_tsflags just before 'sk_stamp'; similar to the above,
>   would possibly reduce the side effects, as most of 'struct sock'
>   layout will be unchanged. Could increase the number of cacheline
>   accessed in the TX path.
>
> I opted for the present solution as it should minimize the side effects
> to other protocols.

Hmm, thanks for the analysis. I will take a look at this today.