X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=doc%2Fguides%2Fprog_guide%2Fvhost_lib.rst;h=92dcdb5879980e9ec309f98c8ef7709513d639d7;hb=a106fcce2cfed0fdee7922594e3199d28dfcce59;hp=0b6eda7836d438d5c4d3b60cef0a5dc73970c208;hpb=0ee5e7fb93aefe9bccb6a9c331cfe27c14bc7ec6;p=dpdk.git diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst index 0b6eda7836..92dcdb5879 100644 --- a/doc/guides/prog_guide/vhost_lib.rst +++ b/doc/guides/prog_guide/vhost_lib.rst @@ -1,101 +1,276 @@ -.. BSD LICENSE - Copyright(c) 2010-2014 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 ============= -The vhost cuse (cuse: user space character device driver) library implements a -vhost cuse driver. It also creates, manages and destroys vhost devices for -corresponding virtio devices in the guest. Vhost supported vSwitch could register -callbacks to this library, which will be called when a vhost device is activated -or deactivated by guest virtual machine. +The vhost library implements a user space virtio net server allowing the user +to manipulate the virtio ring directly. In another words, it allows the user +to fetch/put packets from/to the VM virtio net device. To achieve this, a +vhost library should be able to: + +* Access the guest memory: + + For QEMU, this is done by using the ``-object memory-backend-file,share=on,...`` + option. Which means QEMU will create a file to serve as the guest RAM. + The ``share=on`` option allows another process to map that file, which + means it can access the guest RAM. + +* Know all the necessary information about the vring: + + Information such as where the available ring is stored. Vhost defines some + 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 driver registration +The following is an overview of some key Vhost API functions: + +* ``rte_vhost_driver_register(path, flags)`` + + This function registers a vhost driver into the system. ``path`` specifies + the Unix domain socket file path. + + Currently supported flags are: + + - ``RTE_VHOST_USER_CLIENT`` + + DPDK vhost-user will act as the client when this flag is given. See below + for an explanation. + + - ``RTE_VHOST_USER_NO_RECONNECT`` + + When DPDK vhost-user acts as the client it will keep trying to reconnect + to the server (QEMU) until it succeeds. This is useful in two cases: + + * When QEMU is not started yet. + * When QEMU restarts (for example due to a guest OS reboot). + + This reconnect option is enabled by default. However, it can be turned off + by setting this flag. + + - ``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 zero copy in VM2NIC case, guest Tx used vring may be starved if the + PMD driver consume the mbuf but not release them timely. + + For example, i40e driver has an optimization to maximum NIC pipeline which + postpones returning transmitted mbuf until only tx_free_threshold free + descs left. The virtio TX used ring will be starved if the formula + (num_i40e_tx_desc - num_virtio_tx_desc > tx_free_threshold) is true, since + i40e will not return back mbuf. + + A performance tip for tuning zero copy in VM2NIC case is to adjust the + frequency of mbuf free (i.e. adjust tx_free_threshold of i40e driver) to + balance consumer and producer. + + * 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. + + * zero copy can not work when using vfio-pci with iommu mode currently, this + is because we don't setup iommu dma mapping for guest memory. If you have + to use vfio-pci driver, please insert vfio-pci kernel module in noiommu + mode. + + - ``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. + + 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_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 + currently supported: + + * ``new_device(int vid)`` + + This callback is invoked when a virtio device becomes ready. ``vid`` + is the vhost device ID. + + * ``destroy_device(int vid)`` + + 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. + + * ``features_changed(int vid, uint64_t features)`` + + 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. + + * ``new_connection(int vid)`` + + 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_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. + +* ``rte_vhost_driver_start(path)`` + + This function triggers the vhost-user negotiation. It should be invoked at + the end of initializing a vhost-user driver. + +* ``rte_vhost_enqueue_burst(vid, queue_id, pkts, count)`` + + Transmits (enqueues) ``count`` packets from host to guest. + +* ``rte_vhost_dequeue_burst(vid, queue_id, mbuf_pool, pkts, count)`` + + Receives (dequeues) ``count`` packets from guest, and stored them at ``pkts``. + +* ``rte_vhost_crypto_create(vid, cryptodev_id, sess_mempool, socket_id)`` + + As an extension of new_device(), this function adds virtio-crypto workload + acceleration capability to the device. All crypto workload is processed by + DPDK cryptodev with the device ID of ``cryptodev_id``. + +* ``rte_vhost_crypto_free(vid)`` + + Frees the memory and vhost-user message handlers created in + rte_vhost_crypto_create(). + +* ``rte_vhost_crypto_fetch_requests(vid, queue_id, ops, nb_ops)`` + + Receives (dequeues) ``nb_ops`` virtio-crypto requests from guest, parses + them to DPDK Crypto Operations, and fills the ``ops`` with parsing results. + +* ``rte_vhost_crypto_finalize_requests(queue_id, ops, nb_ops)`` + + After the ``ops`` are dequeued from Cryptodev, finalizes the jobs and + notifies the guest(s). + +* ``rte_vhost_crypto_set_zero_copy(vid, option)`` + + Enable or disable zero copy feature of the vhost crypto backend. + +Vhost-user Implementations +-------------------------- + +Vhost-user uses Unix domain sockets for passing messages. This means the DPDK +vhost-user implementation has two options: + +* DPDK vhost-user acts as the server. + + DPDK will create a Unix domain socket server file and listen for + connections from the frontend. + + Note, this is the default mode, and the only mode before DPDK v16.07. + + +* DPDK vhost-user acts as the client. + + Unlike the server mode, this mode doesn't create the socket file; + it just tries to connect to the server (which responses to create the + file instead). + + 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. - rte_vhost_driver_register registers the vhost cuse driver into the system. - Character device file will be created in the /dev directory. - Character device name is specified as the parameter. + .. Note:: + * The "reconnect" feature requires **QEMU v2.7** (or above). -* Vhost session start + * 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. - rte_vhost_driver_session_start starts the vhost session loop. - Vhost cuse session is an infinite blocking loop. - Put the session in a dedicate DPDK thread. +No matter which mode is used, once a connection is established, DPDK +vhost-user will start receiving and processing vhost messages from QEMU. -* Callback register +For messages with a file descriptor, the file descriptor can be used directly +in the vhost process as it is already installed by the Unix domain socket. - Vhost supported vSwitch could call rte_vhost_driver_callback_register to - register two callbacks, new_destory and destroy_device. - When virtio device is activated or deactivated by guest virtual machine, - the callback will be called, then vSwitch could put the device onto data - core or remove the device from data core. +The supported vhost messages are: -* Read/write packets from/to guest virtual machine +* ``VHOST_SET_MEM_TABLE`` +* ``VHOST_SET_VRING_KICK`` +* ``VHOST_SET_VRING_CALL`` +* ``VHOST_SET_LOG_FD`` +* ``VHOST_SET_VRING_ERR`` - rte_vhost_enqueue_burst transmit host packets to guest. - rte_vhost_dequeue_burst receives packets from guest. +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. -* Feature enable/disable +``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. - Now one negotiate-able feature in vhost is merge-able. - vSwitch could enable/disable this feature for performance consideration. +When the socket connection is closed, vhost will destroy the device. -Vhost Implementation --------------------- +Guest memory requirement +------------------------ -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 message from QEMU simulator. +* Memory pre-allocation -When the open call is received, vhost driver will create a vhost device for the -virtio device in the guest. + For non-zerocopy, guest memory pre-allocation is not a must. This can help + save of memory. If users really want the guest memory to be pre-allocated + (e.g., for performance reason), we can add option ``-mem-prealloc`` when + starting QEMU. Or, we can lock all memory at vhost side which will force + memory to be allocated when mmap at vhost side; option --mlockall in + ovs-dpdk is an example in hand. -When 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 guest -virtual machine. Through this virtual address and the QEMU pid, vhost could -find the file QEMU uses to map the guest memory. Vhost maps this file into its -address space, in this way vhost could 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. + For zerocopy, we force the VM memory to be pre-allocated at vhost lib when + mapping the guest memory; and also we need to lock the memory to prevent + pages being swapped out to disk. -The guest virtual machine tells the vhost whether the virtio device is ready -for processing or is de-activated through VHOST_SET_BACKEND message. -The registered callback from vSwitch will be called. +* Memory sharing -When the release call is released, vhost will destroy the device. + Make sure ``share=on`` QEMU option is given. vhost-user will not work with + a QEMU version without shared memory mapping. Vhost supported vSwitch reference --------------------------------- -For how to support vhost in vSwitch, please refer to vhost example in the -DPDK Sample Applications Guide. +For more vhost details and how to support vhost in vSwitch, please refer to +the vhost example in the DPDK Sample Applications Guide.