Re: [REGRESSION][BISECTED] tun/tap & vhost-net: multi-threaded network performance

[Simon Schippers]

On 7/1/26 21:16, Brett Sheffield wrote:
> TL;DR - Commit 1d6e569b7d0c0b2736636749e4be0a27f3cefcb3 causes
> significant performance regressions with TAP interfaces and multithreaded
> network code. Please revert.

Micheal, I am convinced that netdev_tx_stop_queue() and
netdev_tx_wake_queue() are too slow. The communication between the CPUs
is just too slow. We already spent *a lot* of time speeding it up, the
patchset was only merged at v12...

Yes, I would *love* to have qdisc backpressure on by default but I do
not see how anything could speed it up.


*Is there any issue if we introduce IFF_BACKPRESSURE?*
I implemented it and it is a simple patch that only executes the
stopping / waking  if ((tun->flags & IFF_BACKPRESSURE)).
I could submit that to [net] very soon.

Thank you,
Simon