linux-kernel - Re: [PATCH v2] net: phylink: add missing supported link modes for the fixed-link

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Message-ID: <9f9df3b3-ea08-43d7-8075-68b4fe19e6a0@lunn.ch>
Date: Mon, 17 Nov 2025 14:22:57 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Wei Fang <wei.fang@....com>
Cc: "linux@...linux.org.uk" <linux@...linux.org.uk>,
	"hkallweit1@...il.com" <hkallweit1@...il.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"eric@...int.com" <eric@...int.com>,
	"maxime.chevallier@...tlin.com" <maxime.chevallier@...tlin.com>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net: phylink: add missing supported link modes for
 the fixed-link

On Mon, Nov 17, 2025 at 03:23:05AM +0000, Wei Fang wrote:
> > This also seems like two fixes: a regression for the AUTONEG bit, and
> > allowing pause to be set. So maybe this should be two patches?
> 
> As Russell explained in the thread, one patch is enough.
> 
> > 
> > I'm also surprised TCP is collapsing. This is not an unusual setup,
> > e.g. a home wireless network feeding a cable modem. A high speed link
> > feeding a lower speed link. What RTT is there when TCP gets into
> 
> The below result is the RTT when doing the iperf TCtestP
> root@...943evk:~# ./tcping -I swp2 10.193.102.224 5201
> TCPinging 10.193.102.224 on port 5201
> Reply from 10.193.102.224 (10.193.102.224) on port 5201 TCP_conn=2 time=1.004 ms
> Reply from 10.193.102.224 (10.193.102.224) on port 5201 TCP_conn=3 time=0.958 ms

With 1ms ping times, you don't have buffer bloat problems, so that is
not the issue.

I still think you need to look at this some more. Both Russells
comments about it potentially blocking traffic for other ports, and
why TCP is doing so bad, maybe gets some traffic dumps and ask the TCP
experts.

	Andrew