meter: add configuration profile

[dpdk.git] / doc / guides / prog_guide / vhost_lib.rst

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index 14d5e67..18227b6 100644 (file)
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -1,32 +1,5 @@
-..  BSD LICENSE
-    Copyright(c) 2010-2016 Intel Corporation. All rights reserved.
-    All rights reserved.
-
-    Redistribution and use in source and binary forms, with or without
-    modification, are permitted provided that the following conditions
-    are met:
-
-    * Redistributions of source code must retain the above copyright
-    notice, this list of conditions and the following disclaimer.
-    * Redistributions in binary form must reproduce the above copyright
-    notice, this list of conditions and the following disclaimer in
-    the documentation and/or other materials provided with the
-    distribution.
-    * Neither the name of Intel Corporation nor the names of its
-    contributors may be used to endorse or promote products derived
-    from this software without specific prior written permission.
-
-    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+..  SPDX-License-Identifier: BSD-3-Clause
+    Copyright(c) 2010-2016 Intel Corporation.

 
 Vhost Library
 =============
 
 Vhost Library
 =============


@@ -46,40 +19,21 @@ vhost library should be able to:
 * Know all the necessary information about the vring:
 
   Information such as where the available ring is stored. Vhost defines some
 * Know all the necessary information about the vring:
 
   Information such as where the available ring is stored. Vhost defines some

-  messages to tell the backend all the information it needs to know how to
-  manipulate the vring.
-
-Currently, there are two ways to pass these messages and as a result there are
-two Vhost implementations in DPDK: *vhost-cuse* (where the character devices
-are in user space) and *vhost-user*.
-
-Vhost-cuse creates a user space character device and hook to a function ioctl,
-so that all ioctl commands that are sent from the frontend (QEMU) will be
-captured and handled.
-
-Vhost-user creates a Unix domain socket file through which messages are
-passed.
-
-.. Note::
-
-   Since DPDK v2.2, the majority of the development effort has gone into
-   enhancing vhost-user, such as multiple queue, live migration, and
-   reconnect. Thus, it is strongly advised to use vhost-user instead of
-   vhost-cuse.
+  messages (passed through a Unix domain socket file) to tell the backend all
+  the information it needs to know how to manipulate the vring.

 
 
 Vhost API Overview
 ------------------
 
 
 
 Vhost API Overview
 ------------------
 

-The following is an overview of the Vhost API functions:
+The following is an overview of some key Vhost API functions:

 
 * ``rte_vhost_driver_register(path, flags)``
 
 
 * ``rte_vhost_driver_register(path, flags)``
 

-  This function registers a vhost driver into the system. For vhost-cuse, a
-  ``/dev/path`` character device file will be created. For vhost-user server
-  mode, a Unix domain socket file ``path`` will be created.
+  This function registers a vhost driver into the system. ``path`` specifies
+  the Unix domain socket file path.

 
 

-  Currently two flags are supported (these are valid for vhost-user only):
+  Currently supported flags are:

 
   - ``RTE_VHOST_USER_CLIENT``
 
 
   - ``RTE_VHOST_USER_CLIENT``
 


@@ -97,13 +51,59 @@ The following is an overview of the Vhost API functions:
     This reconnect option is enabled by default. However, it can be turned off
     by setting this flag.
 
     This reconnect option is enabled by default. However, it can be turned off
     by setting this flag.
 

-* ``rte_vhost_driver_session_start()``
+  - ``RTE_VHOST_USER_DEQUEUE_ZERO_COPY``
+
+    Dequeue zero copy will be enabled when this flag is set. It is disabled by
+    default.
+
+    There are some truths (including limitations) you might want to know while
+    setting this flag:
+
+    * zero copy is not good for small packets (typically for packet size below
+      512).
+
+    * zero copy is really good for VM2VM case. For iperf between two VMs, the
+      boost could be above 70% (when TSO is enableld).
+
+    * for VM2NIC case, the ``nb_tx_desc`` has to be small enough: <= 64 if virtio
+      indirect feature is not enabled and <= 128 if it is enabled.
+
+      This is because when dequeue zero copy is enabled, guest Tx used vring will
+      be updated only when corresponding mbuf is freed. Thus, the nb_tx_desc
+      has to be small enough so that the PMD driver will run out of available
+      Tx descriptors and free mbufs timely. Otherwise, guest Tx vring would be
+      starved.
+
+    * Guest memory should be backended with huge pages to achieve better
+      performance. Using 1G page size is the best.
+
+      When dequeue zero copy is enabled, the guest phys address and host phys
+      address mapping has to be established. Using non-huge pages means far
+      more page segments. To make it simple, DPDK vhost does a linear search
+      of those segments, thus the fewer the segments, the quicker we will get
+      the mapping. NOTE: we may speed it by using tree searching in future.
+
+  - ``RTE_VHOST_USER_IOMMU_SUPPORT``
+
+    IOMMU support will be enabled when this flag is set. It is disabled by
+    default.
+
+    Enabling this flag makes possible to use guest vIOMMU to protect vhost
+    from accessing memory the virtio device isn't allowed to, when the feature
+    is negotiated and an IOMMU device is declared.

 
 

-  This function starts the vhost session loop to handle vhost messages. It
-  starts an infinite loop, therefore it should be called in a dedicated
-  thread.
+    However, this feature enables vhost-user's reply-ack protocol feature,
+    which implementation is buggy in Qemu v2.7.0-v2.9.0 when doing multiqueue.
+    Enabling this flag with these Qemu version results in Qemu being blocked
+    when multiple queue pairs are declared.

 
 

-* ``rte_vhost_driver_callback_register(virtio_net_device_ops)``
+* ``rte_vhost_driver_set_features(path, features)``
+
+  This function sets the feature bits the vhost-user driver supports. The
+  vhost-user driver could be vhost-user net, yet it could be something else,
+  say, vhost-user SCSI.
+
+* ``rte_vhost_driver_callback_register(path, vhost_device_ops)``

 
   This function registers a set of callbacks, to let DPDK applications take
   the appropriate action when some events happen. The following events are
 
   This function registers a set of callbacks, to let DPDK applications take
   the appropriate action when some events happen. The following events are


@@ -111,63 +111,57 @@ The following is an overview of the Vhost API functions:
 
   * ``new_device(int vid)``
 
 
   * ``new_device(int vid)``
 

-    This callback is invoked when a virtio net device becomes ready. ``vid``
-    is the virtio net device ID.
+    This callback is invoked when a virtio device becomes ready. ``vid``
+    is the vhost device ID.

 
   * ``destroy_device(int vid)``
 
 
   * ``destroy_device(int vid)``
 

-    This callback is invoked when a virtio net device shuts down (or when the
-    vhost connection is broken).
+    This callback is invoked when a virtio device is paused or shut down.

 
   * ``vring_state_changed(int vid, uint16_t queue_id, int enable)``
 
     This callback is invoked when a specific queue's state is changed, for
     example to enabled or disabled.
 
 
   * ``vring_state_changed(int vid, uint16_t queue_id, int enable)``
 
     This callback is invoked when a specific queue's state is changed, for
     example to enabled or disabled.
 

-* ``rte_vhost_enqueue_burst(vid, queue_id, pkts, count)``
+  * ``features_changed(int vid, uint64_t features)``

 
 

-  Transmits (enqueues) ``count`` packets from host to guest.
+    This callback is invoked when the features is changed. For example,
+    ``VHOST_F_LOG_ALL`` will be set/cleared at the start/end of live
+    migration, respectively.

 
 

-* ``rte_vhost_dequeue_burst(vid, queue_id, mbuf_pool, pkts, count)``
+  * ``new_connection(int vid)``

 
 

-  Receives (dequeues) ``count`` packets from guest, and stored them at ``pkts``.
+    This callback is invoked on new vhost-user socket connection. If DPDK
+    acts as the server the device should not be deleted before
+    ``destroy_connection`` callback is received.
+
+  * ``destroy_connection(int vid)``
+
+    This callback is invoked when vhost-user socket connection is closed.
+    It indicates that device with id ``vid`` is no longer in use and can be
+    safely deleted.

 
 

-* ``rte_vhost_feature_disable/rte_vhost_feature_enable(feature_mask)``
+* ``rte_vhost_driver_disable/enable_features(path, features))``

 
   This function disables/enables some features. For example, it can be used to
   disable mergeable buffers and TSO features, which both are enabled by
   default.
 
 
   This function disables/enables some features. For example, it can be used to
   disable mergeable buffers and TSO features, which both are enabled by
   default.
 

+* ``rte_vhost_driver_start(path)``

 
 

-Vhost Implementations
----------------------
+  This function triggers the vhost-user negotiation. It should be invoked at
+  the end of initializing a vhost-user driver.

 
 

-Vhost-cuse implementation
-~~~~~~~~~~~~~~~~~~~~~~~~~
-
-When vSwitch registers the vhost driver, it will register a cuse device driver
-into the system and creates a character device file. This cuse driver will
-receive vhost open/release/IOCTL messages from the QEMU simulator.
-
-When the open call is received, the vhost driver will create a vhost device
-for the virtio device in the guest.
+* ``rte_vhost_enqueue_burst(vid, queue_id, pkts, count)``

 
 

-When the ``VHOST_SET_MEM_TABLE`` ioctl is received, vhost searches the memory
-region to find the starting user space virtual address that maps the memory of
-the guest virtual machine. Through this virtual address and the QEMU pid,
-vhost can find the file QEMU uses to map the guest memory. Vhost maps this
-file into its address space, in this way vhost can fully access the guest
-physical memory, which means vhost could access the shared virtio ring and the
-guest physical address specified in the entry of the ring.
+  Transmits (enqueues) ``count`` packets from host to guest.

 
 

-The guest virtual machine tells the vhost whether the virtio device is ready
-for processing or is de-activated through the ``VHOST_NET_SET_BACKEND``
-message. The registered callback from vSwitch will be called.
+* ``rte_vhost_dequeue_burst(vid, queue_id, mbuf_pool, pkts, count)``

 
 

-When the release call is made, vhost will destroy the device.
+  Receives (dequeues) ``count`` packets from guest, and stored them at ``pkts``.

 
 

-Vhost-user implementation
-~~~~~~~~~~~~~~~~~~~~~~~~~
+Vhost-user Implementations
+--------------------------

 
 Vhost-user uses Unix domain sockets for passing messages. This means the DPDK
 vhost-user implementation has two options:
 
 Vhost-user uses Unix domain sockets for passing messages. This means the DPDK
 vhost-user implementation has two options:


@@ -189,7 +183,12 @@ vhost-user implementation has two options:
   When the DPDK vhost-user application restarts, DPDK vhost-user will try to
   connect to the server again. This is how the "reconnect" feature works.
 
   When the DPDK vhost-user application restarts, DPDK vhost-user will try to
   connect to the server again. This is how the "reconnect" feature works.
 

-  Note: the "reconnect" feature requires **QEMU v2.7** (or above).
+  .. Note::
+     * The "reconnect" feature requires **QEMU v2.7** (or above).
+
+     * The vhost supported features must be exactly the same before and
+       after the restart. For example, if TSO is disabled and then enabled,
+       nothing will work and issues undefined might happen.

 
 No matter which mode is used, once a connection is established, DPDK
 vhost-user will start receiving and processing vhost messages from QEMU.
 
 No matter which mode is used, once a connection is established, DPDK
 vhost-user will start receiving and processing vhost messages from QEMU.


@@ -209,8 +208,6 @@ For ``VHOST_SET_MEM_TABLE`` message, QEMU will send information for each
 memory region and its file descriptor in the ancillary data of the message.
 The file descriptor is used to map that region.
 
 memory region and its file descriptor in the ancillary data of the message.
 The file descriptor is used to map that region.
 

-There is no ``VHOST_NET_SET_BACKEND`` message as in vhost-cuse to signal
-whether the virtio device is ready or stopped. Instead,

 ``VHOST_SET_VRING_KICK`` is used as the signal to put the vhost device into
 the data plane, and ``VHOST_GET_VRING_BASE`` is used as the signal to remove
 the vhost device from the data plane.
 ``VHOST_SET_VRING_KICK`` is used as the signal to put the vhost device into
 the data plane, and ``VHOST_GET_VRING_BASE`` is used as the signal to remove
 the vhost device from the data plane.