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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Rob Herring , Krzysztof Kozlowski , Florian Fainelli , Maxime Chevallier , Kory Maincent , Lukasz Majewski , Jonathan Corbet , Donald Hunter , Vadim Fedorenko , Jiri Pirko , Vladimir Oltean , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend Cc: kernel@pengutronix.de, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Russell King , Divya.Koppera@microchip.com, Sabrina Dubroca , Stanislav Fomichev Subject: Re: [PATCH net-next v5 1/1] Documentation: net: add flow control guide and document ethtool API Message-ID: References: <20250918051538.3651265-1-o.rempel@pengutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="oV2pbrsk+dCJ8esC" Content-Disposition: inline In-Reply-To: <20250918051538.3651265-1-o.rempel@pengutronix.de> --oV2pbrsk+dCJ8esC Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Sep 18, 2025 at 07:15:38AM +0200, Oleksij Rempel wrote: > +* **How it works**: To inhibit incoming data, a receiving device can for= ce a > + collision on the line. When the sending station detects this collisi= on, it > + terminates its transmission, sends a "jam" signal, and then executes= the > + "Collision backoff and retransmission" procedure as defined in IEEE = 802.3, > + Section 4.2.3.2.5. This algorithm makes the sender wait for a random > + period before attempting to retransmit. By repeatedly forcing collis= ions, > + the receiver can effectively throttle the sender's transmission rate. Please align the bullet list text. I see hanging indent instead there in htmldocs output. > +* **What it is**: A standard Ethernet frame with a globally reserved > + destination MAC address (``01-80-C2-00-00-01``). This address is in = a range > + that standard IEEE 802.1D-compliant bridges do not forward. However,= some > + unmanaged or misconfigured bridges have been reported to forward the= se > + frames, which can disrupt flow control across a network. > + > +* **How it works**: The frame contains a MAC Control opcode for PAUSE > + (``0x0001``) and a ``pause_time`` value, telling the sender how long= to > + wait before sending more data frames. This time is specified in unit= s of > + "pause quantum", where one quantum is the time it takes to transmit = 512 bits. > + For example, one pause quantum is 51.2 microseconds on a 10 Mbit/s l= ink, > + and 512 nanoseconds on a 1 Gbit/s link. A ``pause_time`` of zero ind= icates > + that the transmitter can resume transmission, even if a previous non= -zero > + pause time has not yet elapsed. Same here. > +* **What it is**: PFC allows a receiver to pause traffic for one or more= of the > + 8 standard priority levels without stopping traffic for other priori= ties. > + This is critical in data center environments for protocols that cann= ot > + tolerate packet loss due to congestion (e.g., Fibre Channel over Eth= ernet > + or RoCE). > + > +* **How it works**: PFC uses a specific PAUSE frame format. It shares th= e same > + globally reserved destination MAC address (``01-80-C2-00-00-01``) as= legacy > + PAUSE frames but uses a unique opcode (``0x0101``). The frame payload > + contains two key fields: > + > + - **``priority_enable_vector``**: An 8-bit mask where each bit corre= sponds to > + one of the 8 priorities. If a bit is set to 1, it means the pause = time > + for that priority is active. > + - **``time_vector``**: A list of eight 2-octet fields, one for each = priority. > + Each field specifies the ``pause_time`` for its corresponding prio= rity, > + measured in units of ``pause_quanta`` (the time to transmit 512 bi= ts). Ditto. Thanks. --=20 An old man doll... just what I always wanted! - Clara --oV2pbrsk+dCJ8esC Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQSSYQ6Cy7oyFNCHrUH2uYlJVVFOowUCaMvF7gAKCRD2uYlJVVFO o79lAQDH8IV49DcW+hwiMg+vNiZyA5vrPzmGSVHqpDc1ILyIHgD9Eh67ub4hbJGg Spts2kxJlXc/zM5nT0aVpERot9Sgjw0= =ajh1 -----END PGP SIGNATURE----- --oV2pbrsk+dCJ8esC--