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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483a9caadedsm166131135e9.10.2026.02.23.07.13.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Feb 2026 07:13:59 -0800 (PST) Date: Mon, 23 Feb 2026 15:13:58 +0000 From: David Laight To: Laurent Vivier Cc: Koen Vandeputte , oneukum@suse.com, andrew+netdev@lunn.ch, Eric Dumazet , kuba@kernel.org, pabeni@redhat.com, netdev , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: commit 662dc80a5e86 breaks rmnet over usb Message-ID: <20260223151358.0efc263d@pumpkin> In-Reply-To: <95ccf5a6-975b-4543-80a3-595f1ee20543@redhat.com> References: <95ccf5a6-975b-4543-80a3-595f1ee20543@redhat.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 23 Feb 2026 15:08:41 +0100 Laurent Vivier wrote: ... > It's weird to be able to set an MTU that is not supported by the hardware. > > To restore performance I think the rx_usb_size should be decoupled from MTU max in qmi_wwan. A lot of 'usbnet' drivers support usb packets that contain multiple ethernet frames. IIRC (I looked at this code quite a few years ago) some (all?) lie very badly about the skb 'true_size' of receive packets - putting in the frame size even though it is sat in 16kb+ of kernel memory. In reality the driver want to receive the 'stream' of usb packets and debatch it directly into ethernet frames without going though the 'urb' buffers at all. ISTR that would be possible with the xhci/usb3 hardware, but would be a massive re-write of parts of the stack. I was only trying (and I mean failing) to get 100M working reliably. Project got canned for other reasons. David