Re: [PATCH net v2 0/2] tcp_metrics: fix hanlding of route options

[Petr Tesarik]

On Fri, 20 Jun 2025 06:24:23 -0700
Eric Dumazet <edumazet@xxxxxxxxxx> wrote:

> On Fri, Jun 20, 2025 at 5:57 AM Petr Tesarik <ptesarik@xxxxxxxx> wrote:
> >
> > I ran into a couple of issues while trying to tweak TCP congestion
> > avoidance to analyze a potential performance regression. It turns out
> > that overriding the parameters with ip-route(8) does not work as
> > expected and appears to be buggy.  
> 
> Hi Petr
> 
> Could you add packetdrill tests as well ?

Glad to do that. But it will be my first time. ;-) Is there a tutorial?
I looked under Documentation/ and didn't see anything.

> Given this could accidentally break user setups, maybe net-next would be safer.

Yeah, you're right. Technically, it is a bugfix, but if it's been
broken for more than a decade without anyone complaining, it can't be
super-urgent.

> Some of us disable tcp_metrics, because metrics used one minute (or
> few seconds) in the past are not very helpful, and source of
> confusion.
> 
> (/proc/sys/net/ipv4/tcp_no_metrics_save set to 1)

Yes, I know about that one. FWIW it didn't help at all in my case,
because then the value from the routing table was ALWAYS ignored...

Petr T