From: Yuanhan Liu Date: Sun, 9 Oct 2016 07:27:58 +0000 (+0800) Subject: vhost: add a flag to enable dequeue zero copy X-Git-Tag: spdx-start~5620 X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=9ba1e744ab6516c4ba593e60b56af16e443d8dbc;p=dpdk.git vhost: add a flag to enable dequeue zero copy Dequeue zero copy is disabled by default. Here add a new flag ``RTE_VHOST_USER_DEQUEUE_ZERO_COPY`` to explictily enable it. Signed-off-by: Yuanhan Liu Reviewed-by: Maxime Coquelin Tested-by: Qian Xu --- diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst index 6b0c6b2649..573a318162 100644 --- a/doc/guides/prog_guide/vhost_lib.rst +++ b/doc/guides/prog_guide/vhost_lib.rst @@ -79,7 +79,7 @@ The following is an overview of the Vhost API functions: ``/dev/path`` character device file will be created. For vhost-user server mode, a Unix domain socket file ``path`` will be created. - Currently two flags are supported (these are valid for vhost-user only): + Currently supported flags are (these are valid for vhost-user only): - ``RTE_VHOST_USER_CLIENT`` @@ -97,6 +97,38 @@ 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. + - ``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. + + The 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_driver_session_start()`` This function starts the vhost session loop to handle vhost messages. It diff --git a/doc/guides/rel_notes/release_16_11.rst b/doc/guides/rel_notes/release_16_11.rst index 51fc7075a4..98914e3fe2 100644 --- a/doc/guides/rel_notes/release_16_11.rst +++ b/doc/guides/rel_notes/release_16_11.rst @@ -45,6 +45,18 @@ New Features in an mbuf chain and retrieve its packet type by software. * Added new functions ``rte_get_ptype_*()`` to dump a packet type as a string. +* **Added vhost-user dequeue zero copy support** + + The copy in dequeue path is saved, which is meant to improve the performance. + In the VM2VM case, the boost is quite impressive. The bigger the packet size, + the bigger performance boost you may get. However, for VM2NIC case, there + are some limitations, yet the boost is not that impressive as VM2VM case. + It may even drop quite a bit for small packets. + + For such reason, this feature is disabled by default. It can be enabled when + ``RTE_VHOST_USER_DEQUEUE_ZERO_COPY`` flag is given. Check the vhost section + at programming guide for more information. + * **Added vhost-user indirect descriptors support.** If indirect descriptor feature is negotiated, each packet sent by the guest diff --git a/lib/librte_vhost/rte_virtio_net.h b/lib/librte_vhost/rte_virtio_net.h index a88aecdc47..c53ff64176 100644 --- a/lib/librte_vhost/rte_virtio_net.h +++ b/lib/librte_vhost/rte_virtio_net.h @@ -53,6 +53,7 @@ #define RTE_VHOST_USER_CLIENT (1ULL << 0) #define RTE_VHOST_USER_NO_RECONNECT (1ULL << 1) +#define RTE_VHOST_USER_DEQUEUE_ZERO_COPY (1ULL << 2) /* Enum for virtqueue management. */ enum {VIRTIO_RXQ, VIRTIO_TXQ, VIRTIO_QNUM}; diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c index bf03f84d33..967cb65379 100644 --- a/lib/librte_vhost/socket.c +++ b/lib/librte_vhost/socket.c @@ -62,6 +62,7 @@ struct vhost_user_socket { int connfd; bool is_server; bool reconnect; + bool dequeue_zero_copy; }; struct vhost_user_connection { @@ -203,6 +204,9 @@ vhost_user_add_connection(int fd, struct vhost_user_socket *vsocket) size = strnlen(vsocket->path, PATH_MAX); vhost_set_ifname(vid, vsocket->path, size); + if (vsocket->dequeue_zero_copy) + vhost_enable_dequeue_zero_copy(vid); + RTE_LOG(INFO, VHOST_CONFIG, "new device, handle is %d\n", vid); vsocket->connfd = fd; @@ -499,6 +503,7 @@ rte_vhost_driver_register(const char *path, uint64_t flags) memset(vsocket, 0, sizeof(struct vhost_user_socket)); vsocket->path = strdup(path); vsocket->connfd = -1; + vsocket->dequeue_zero_copy = flags & RTE_VHOST_USER_DEQUEUE_ZERO_COPY; if ((flags & RTE_VHOST_USER_CLIENT) != 0) { vsocket->reconnect = !(flags & RTE_VHOST_USER_NO_RECONNECT); diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c index dbf5d1b862..469117a2cf 100644 --- a/lib/librte_vhost/vhost.c +++ b/lib/librte_vhost/vhost.c @@ -291,6 +291,16 @@ vhost_set_ifname(int vid, const char *if_name, unsigned int if_len) dev->ifname[sizeof(dev->ifname) - 1] = '\0'; } +void +vhost_enable_dequeue_zero_copy(int vid) +{ + struct virtio_net *dev = get_device(vid); + + if (dev == NULL) + return; + + dev->dequeue_zero_copy = 1; +} int rte_vhost_get_numa_node(int vid) diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h index be8a398d9b..53dbf33cb0 100644 --- a/lib/librte_vhost/vhost.h +++ b/lib/librte_vhost/vhost.h @@ -278,6 +278,7 @@ void vhost_destroy_device(int); int alloc_vring_queue_pair(struct virtio_net *dev, uint32_t qp_idx); void vhost_set_ifname(int, const char *if_name, unsigned int if_len); +void vhost_enable_dequeue_zero_copy(int vid); /* * Backend-specific cleanup. Defined by vhost-cuse and vhost-user.