Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. SPDX-License-Identifier: GPL-2.0
+
+===========================================
+HOWTO for multiqueue network device support
+===========================================
+
+Section 1: Base driver requirements for implementing multiqueue support
+=======================================================================
+
+Intro: Kernel support for multiqueue devices
+---------------------------------------------------------
+
+Kernel support for multiqueue devices is always present.
+
+Base drivers are required to use the new alloc_etherdev_mq() or
+alloc_netdev_mq() functions to allocate the subqueues for the device.  The
+underlying kernel API will take care of the allocation and deallocation of
+the subqueue memory, as well as netdev configuration of where the queues
+exist in memory.
+
+The base driver will also need to manage the queues as it does the global
+netdev->queue_lock today.  Therefore base drivers should use the
+netif_{start|stop|wake}_subqueue() functions to manage each queue while the
+device is still operational.  netdev->queue_lock is still used when the device
+comes online or when it's completely shut down (unregister_netdev(), etc.).
+
+
+Section 2: Qdisc support for multiqueue devices
+===============================================
+
+Currently two qdiscs are optimized for multiqueue devices.  The first is the
+default pfifo_fast qdisc.  This qdisc supports one qdisc per hardware queue.
+A new round-robin qdisc, sch_multiq also supports multiple hardware queues. The
+qdisc is responsible for classifying the skb's and then directing the skb's to
+bands and queues based on the value in skb->queue_mapping.  Use this field in
+the base driver to determine which queue to send the skb to.
+
+sch_multiq has been added for hardware that wishes to avoid head-of-line
+blocking.  It will cycle though the bands and verify that the hardware queue
+associated with the band is not stopped prior to dequeuing a packet.
+
+On qdisc load, the number of bands is based on the number of queues on the
+hardware.  Once the association is made, any skb with skb->queue_mapping set,
+will be queued to the band associated with the hardware queue.
+
+
+Section 3: Brief howto using MULTIQ for multiqueue devices
+==========================================================
+
+The userspace command 'tc,' part of the iproute2 package, is used to configure
+qdiscs.  To add the MULTIQ qdisc to your network device, assuming the device
+is called eth0, run the following command::
+
+    # tc qdisc add dev eth0 root handle 1: multiq
+
+The qdisc will allocate the number of bands to equal the number of queues that
+the device reports, and bring the qdisc online.  Assuming eth0 has 4 Tx
+queues, the band mapping would look like::
+
+    band 0 => queue 0
+    band 1 => queue 1
+    band 2 => queue 2
+    band 3 => queue 3
+
+Traffic will begin flowing through each queue based on either the simple_tx_hash
+function or based on netdev->select_queue() if you have it defined.
+
+The behavior of tc filters remains the same.  However a new tc action,
+skbedit, has been added.  Assuming you wanted to route all traffic to a
+specific host, for example 192.168.0.3, through a specific queue you could use
+this action and establish a filter such as::
+
+    tc filter add dev eth0 parent 1: protocol ip prio 1 u32 \
+	    match ip dst 192.168.0.3 \
+	    action skbedit queue_mapping 3
+
+:Author: Alexander Duyck <alexander.h.duyck@intel.com>
+:Original Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com>