From: "Michael S. Tsirkin" <mst@redhat.com>
To: Simon Schippers <simon.schippers@tu-dortmund.de>
Cc: Jakub Kicinski <kuba@kernel.org>,
Tim Gebauer <tim.gebauer@tu-dortmund.de>,
Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
Jason Wang <jasowang@redhat.com>,
Andrew Lunn <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
linux-kernel@vger.kernel.org,
Brett Sheffield <bacs@librecast.net>,
regressions@lists.linux.dev, netdev@vger.kernel.org
Subject: Re: [REGRESSION][BISECTED] tun/tap & vhost-net: multi-threaded network performance
Date: Fri, 3 Jul 2026 07:55:38 -0400 [thread overview]
Message-ID: <20260703075438-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <a1bae349-61a1-4c65-a531-179850576642@tu-dortmund.de>
On Fri, Jul 03, 2026 at 12:41:19PM +0200, Simon Schippers wrote:
> 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
Pls go ahead.
--
MST
prev parent reply other threads:[~2026-07-03 11:55 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-01 19:16 [REGRESSION][BISECTED] tun/tap & vhost-net: multi-threaded network performance Brett Sheffield
2026-07-01 20:56 ` Michael S. Tsirkin
2026-07-02 7:24 ` Simon Schippers
2026-07-02 7:42 ` Michael S. Tsirkin
2026-07-02 8:01 ` Simon Schippers
2026-07-02 11:07 ` Brett Sheffield
2026-07-02 22:44 ` Michael S. Tsirkin
2026-07-03 10:34 ` Simon Schippers
2026-07-02 22:55 ` Michael S. Tsirkin
2026-07-03 10:35 ` Simon Schippers
2026-07-03 14:13 ` Brett Sheffield
2026-07-03 14:19 ` Michael S. Tsirkin
2026-07-03 10:41 ` Simon Schippers
2026-07-03 11:55 ` Michael S. Tsirkin [this message]
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