netdev - Re: [PATCH net-next 00/11] tcp: receive side improvements

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: <a7ff9548-ec75-40be-9770-e19308c5389e@iogearbox.net>
Date: Thu, 22 May 2025 16:03:07 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>,
 Rick Jones <jonesrick@...gle.com>, Wei Wang <weiwan@...gle.com>,
 netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 00/11] tcp: receive side improvements

Hi Eric,

On 5/13/25 9:39 PM, Eric Dumazet wrote:
> We have set tcp_rmem[2] to 15 MB for about 8 years at Google,
> but had some issues for high speed flows on very small RTT.

Are there plans to bump/modernize the rmem_default and rmem_max defaults,
too? Looks like last time it was done back in commit eaa72dc4748 ("neigh:
increase queue_len_bytes to match wmem_default"). Fwiw, we've experienced
deployments where vxlan/geneve is being used for E/W to be affected to hit
the distro default limits leading to UDP drops for TCP traffic. Would it
make sense to move these e.g. to 4MB as well or do you have used another
heuristic which worked well over the years?

> TCP rx autotuning has a tendency to overestimate the RTT,
> thus tp->rcvq_space.space and sk->sk_rcvbuf.
> 
> This makes TCP receive queues much bigger than necessary,
> to a point cpu caches are evicted before application can
> copy the data, on cpus using DDIO.
> 
> This series aims to fix this.
> 
> - First patch adds tcp_rcvbuf_grow() tracepoint, which was very
>    convenient to study the various issues fixed in this series.
> 
> - Seven patches fix receiver autotune issues.
> 
> - Two patches fix sender side issues.
> 
> - Final patch increases tcp_rmem[2] so that TCP speed over WAN
>    can meet modern needs.
> 
> Tested on a 200Gbit NIC, average max throughput of a single flow:
> 
> Before:
>   73593 Mbit.
> 
> After:
>   122514 Mbit.

Thanks,
Daniel