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From: Brett Sheffield <brett@librecast.net>
To: Simon Schippers <simon.schippers@tu-dortmund.de>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	Jason Wang <jasowangio@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	netdev@vger.kernel.org, Simon Horman <horms@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Andrew Lunn <andrew+netdev@lunn.ch>,
	Tim Gebauer <tim.gebauer@tu-dortmund.de>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] tun/tap & vhost-net: make qdisc backpressure opt-in via IFF_BACKPRESSURE
Date: Sat, 4 Jul 2026 13:58:52 +0200	[thread overview]
Message-ID: <akj1fObc_PSd4oha@karahi.librecast.net> (raw)
In-Reply-To: <20260704112058.95421-1-simon.schippers@tu-dortmund.de>

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@librecast.net>

Cheers,


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

  reply	other threads:[~2026-07-04 11:59 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-07-04 11:20 [PATCH net] tun/tap & vhost-net: make qdisc backpressure opt-in via IFF_BACKPRESSURE Simon Schippers
2026-07-04 11:58 ` Brett Sheffield [this message]
2026-07-04 12:28 ` Michael S. Tsirkin
2026-07-04 12:52 ` Michael S. Tsirkin
2026-07-06  6:46 ` Simon Schippers

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