On Tue, Jul 28, 2026 at 11:22:36AM +0200, 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 causes a
> significant throughput drop in an IPv6 multicast testcase. The regression
> can be pinpointed to multiple iperf3 TCP threads sending: for 8 threads
> the throughput dropped from 13.5 Gbit/s to 9.13 Gbit/s.
>
> Therefore this series reverts the qdisc backpressure work.
>
> Making the backpressure opt-in via a new IFF_BACKPRESSURE flag was
> proposed in [1], but a new IFF_* flag needs more review scrutiny than is
> available at the moment, so a revert was requested instead. The opt-in
> will be resubmitted for net-next later.
Acked-by: Michael S. Tsirkin <[email protected]>
Thanks!
> [1] Link:
> https://lore.kernel.org/netdev/[email protected]/
>
> Reported-by: Brett Sheffield <[email protected]>
> Closes: https://lore.kernel.org/netdev/[email protected]/
>
> Simon Schippers (4):
> Revert "tun/tap & vhost-net: avoid ptr_ring tail-drop when a qdisc is
> present"
> Revert "ptr_ring: move free-space check into separate helper"
> Revert "vhost-net: wake queue of tun/tap after ptr_ring consume"
> Revert "tun/tap: add ptr_ring consume helper with netdev queue wakeup"
>
> drivers/net/tun.c | 109 +++------------------------------------
> drivers/vhost/net.c | 21 +++-----
> include/linux/if_tun.h | 3 --
> include/linux/ptr_ring.h | 20 +------
> 4 files changed, 14 insertions(+), 139 deletions(-)
>
>
> base-commit: b14361aca6350ff7907b0e9903c7b94dc7d5d4a0
> --
> 2.43.0
