Re: [PATCH net-next 2/2] tcp: add net.ipv4.tcp_rtt_threshold sysctl

[Paolo Abeni <pabeni@redhat.com>]

On 11/18/25 10:22 PM, Eric Dumazet wrote:
> I would perhaps use 8 senders, and force all receivers on one cpu (cpu
> 4 in the following run)
> 
> for i in {1..8}
> do
>  netperf -H host -T,4 -l 100 &
> done
> 
> This would I think show what can happen when receivers can not keep up.

Thanks for the suggestion. I should have understood the receiver needs
to be under stress in the relevant scenario.

With the above setup, on vanilla kernel, the rcvbuf I see is:

min 2134391 max 33554432 avg 12085941

with multiple connections hitting tcp_rmem[2]

with the patched kernel:

min 1192472 max 33554432 avg 4247351

there is a single outlier hitting tcp_rmem[2], and in that case the
connection observes for some samples a rtt just above tcp_rtt_threshold
sysctl/tcp_rcvbuf_low_rtt.

FWIW I guess you can add:

Tested-by: Paolo Abeni <pabeni@redhat.com>

Thanks,

Paolo