Re: [PATCH net] tun/tap & vhost-net: make qdisc backpressure opt-in via IFF_BACKPRESSURE

[Brett Sheffield]

On 2026-07-04 13:20, Simon Schippers wrote:
> Commit 1d6e569b7d0c ("tun/tap & vhost-net: avoid ptr_ring tail-drop
> when a qdisc is present") did not show a relevant performance regression
> in my testing but on Brett Sheffield's librecast testbed it shows a
> significant performance drop. The regression can be pinpointed when
> multiple iperf3 TCP threads are sending. For 8 threads the performance
> dropped from 13.5 Gbit/s to 9.13 Gbit/s. This is the reason why this
> patch makes the qdisc backpressure behavior opt-in.

Thanks Simon.

I've tested and confirmed this fixes the original failing IPv6 multicast (UDP)
test which flagged the problem.

Tested-by: Brett A C Sheffield <bacs@xxxxxxxxxxxxx>

Cheers,


Brett
-- 
Brett Sheffield (he/him)
Librecast - Decentralising the Internet with Multicast
https://librecast.net/
https://blog.brettsheffield.com/