netdev - Re: [PATCH net-next 0/2] tcp: add sysctl_tcp_rto_min

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Date: Wed, 29 May 2024 16:49:39 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Tony Lu <tonylu@...ux.alibaba.com>
Cc: Kevin Yang <yyd@...gle.com>, David Miller <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/2] tcp: add sysctl_tcp_rto_min_us

On Wed, May 29, 2024 at 3:21 PM Tony Lu <tonylu@...ux.alibaba.com> wrote:
>
> On Tue, May 28, 2024 at 05:13:18PM +0000, Kevin Yang wrote:
> > Adding a sysctl knob to allow user to specify a default
> > rto_min at socket init time.
> >
> > After this patch series, the rto_min will has multiple sources:
> > route option has the highest precedence, followed by the
> > TCP_BPF_RTO_MIN socket option, followed by this new
> > tcp_rto_min_us sysctl.
>
> For series:
>
> Reviewed-by: Tony Lu <tonylu@...ux.alibaba.com>
>
> I strongly support those patches. For those who use cgroup v1 and want
> to take effect with simple settings, sysctl is a good way.

It's not a good reason to use sysctl.

If you say so, why not introduce many sysctls to replace setsockopt
operations. For example, introducing a new sysctl to disable delayed
ack to improve the speed of transmission in some cases just for ease
of use? No, it's not right, I believe.

>
> And reducing it is helpful for latency-sensitive applications such as
> Redis, net namespace level sysctl knob is enough.

Sure, these key parameters play a big role in the TCP stack.

>
> >
> > Kevin Yang (2):
> >   tcp: derive delack_max with tcp_rto_min helper
> >   tcp: add sysctl_tcp_rto_min_us
> >
> >  Documentation/networking/ip-sysctl.rst | 13 +++++++++++++
> >  include/net/netns/ipv4.h               |  1 +
> >  net/ipv4/sysctl_net_ipv4.c             |  8 ++++++++
> >  net/ipv4/tcp.c                         |  3 ++-
> >  net/ipv4/tcp_ipv4.c                    |  1 +
> >  net/ipv4/tcp_output.c                  | 11 ++---------
> >  6 files changed, 27 insertions(+), 10 deletions(-)
> >
> > --
> > 2.45.1.288.g0e0cd299f1-goog
> >
>