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[80.230.35.22]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d7f653cd6sm367623105e9.9.2026.01.12.03.19.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 03:19:28 -0800 (PST) Date: Mon, 12 Jan 2026 06:19:25 -0500 From: "Michael S. Tsirkin" To: Simon Schippers Cc: Jason Wang , willemdebruijn.kernel@gmail.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, eperezma@redhat.com, leiyang@redhat.com, stephen@networkplumber.org, jon@nutanix.com, tim.gebauer@tu-dortmund.de, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev Subject: Re: [PATCH net-next v7 9/9] tun/tap & vhost-net: avoid ptr_ring tail-drop when qdisc is present Message-ID: <20260112061831-mutt-send-email-mst@kernel.org> References: <20260107210448.37851-1-simon.schippers@tu-dortmund.de> <20260107210448.37851-10-simon.schippers@tu-dortmund.de> <900c364b-f5ca-4458-a711-bf3e0433b537@tu-dortmund.de> <20260111233129-mutt-send-email-mst@kernel.org> <55bcb1ec-bdbb-44aa-8fa0-470916e986aa@tu-dortmund.de> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55bcb1ec-bdbb-44aa-8fa0-470916e986aa@tu-dortmund.de> On Mon, Jan 12, 2026 at 12:17:12PM +0100, Simon Schippers wrote: > On 1/12/26 05:33, Michael S. Tsirkin wrote: > > On Fri, Jan 09, 2026 at 11:14:54AM +0100, Simon Schippers wrote: > >> Am I not allowed to stop the queue and then return NETDEV_TX_BUSY? > > > > We jump through a lot of hoops in virtio_net to avoid using > > NETDEV_TX_BUSY because that bypasses all the net/ cleverness. > > Given your patches aim to improve precisely ring full, > > I would say stopping proactively before NETDEV_TX_BUSY > > should be a priority. > > > > I already proactively stop here with the approach you proposed in > the v6. > Or am I missing something (apart from the xdp path)? Yes, I am just answering the general question you posed. > > And yes I also dislike returning NETDEV_TX_BUSY but I do not see how > this can be prevented with lltx enabled. Preventing NETDEV_TX_BUSY 100% of the time is not required. It's there to handle races. -- MST