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[80.230.68.31]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-493ccd9d607sm60793295e9.2.2026.07.03.04.55.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jul 2026 04:55:41 -0700 (PDT) Date: Fri, 3 Jul 2026 07:55:38 -0400 From: "Michael S. Tsirkin" To: Simon Schippers Cc: Jakub Kicinski , Tim Gebauer , Willem de Bruijn , Jason Wang , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , linux-kernel@vger.kernel.org, Brett Sheffield , regressions@lists.linux.dev, netdev@vger.kernel.org Subject: Re: [REGRESSION][BISECTED] tun/tap & vhost-net: multi-threaded network performance Message-ID: <20260703075438-mutt-send-email-mst@kernel.org> References: Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: uUuhb_VdQxDjvfNwnx7N15I_FPpIbBJxWqTvHXz_XOM_1783079743 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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