Hi.
Not a full review. Few comments inline.
Best regards, Ilya Maximets.
On 15.10.2019 18:17, Flavio Leitner wrote:
The rte_vhost_dequeue_burst supports two ways of dequeuing data.
If the data fits into a buffer, then all data is copied and a
single linear buffer is returned. Otherwise it allocates
additional mbufs and chains them together to return a multiple
segments mbuf.
While that covers most use cases, it forces applications that
need to work with larger data sizes to support multiple segments
mbufs. The non-linear characteristic brings complexity and
performance implications to the application.
To resolve the issue, add support to attach external buffer
to a pktmbuf and let the host provide during registration if
attaching an external buffer to pktmbuf is supported and if
only linear buffer are supported.
Signed-off-by: Flavio Leitner <f...@sysclose.org>
---
doc/guides/prog_guide/vhost_lib.rst | 35 +++++++++
lib/librte_vhost/rte_vhost.h | 4 +
lib/librte_vhost/socket.c | 22 ++++++
lib/librte_vhost/vhost.c | 22 ++++++
lib/librte_vhost/vhost.h | 4 +
lib/librte_vhost/virtio_net.c | 109 ++++++++++++++++++++++++----
6 files changed, 182 insertions(+), 14 deletions(-)
- Changelog:
v4:
- allow to use pktmbuf if there is exact space
- removed log message if the buffer is too big
- fixed the length to include align padding
- free allocated buf if shinfo fails
v3:
- prevent the new features to be used with zero copy
- fixed sizeof() usage
- fixed log msg indentation
- removed/replaced asserts
- used the correct virt2iova function
- fixed the patch's title
- OvS PoC code:
https://github.com/fleitner/ovs/tree/rte_malloc-v3
v2:
- Used rte_malloc() instead of another mempool as suggested by Shahaf.
- Added the documentation section.
- Using driver registration to negotiate the features.
- OvS PoC code:
https://github.com/fleitner/ovs/commit/8fc197c40b1d4fda331686a7b919e9e2b670dda7
diff --git a/doc/guides/prog_guide/vhost_lib.rst
b/doc/guides/prog_guide/vhost_lib.rst
index fc3ee4353..07e40e3c5 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -117,6 +117,41 @@ The following is an overview of some key Vhost API
functions:
Enabling this flag should only be done when the calling application does
not pre-fault the guest shared memory, otherwise migration would fail.
+ - ``RTE_VHOST_USER_LINEARBUF_SUPPORT``
+
+ Enabling this flag forces vhost dequeue function to only provide linear
+ pktmbuf (no multi-segmented pktmbuf).
+
+ The vhost library by default provides a single pktmbuf for given a
+ packet, but if for some reason the data doesn't fit into a single
+ pktmbuf (e.g., TSO is enabled), the library will allocate additional
+ pktmbufs from the same mempool and chain them together to create a
+ multi-segmented pktmbuf.
+
+ However, the vhost application needs to support multi-segmented format.
+ If the vhost application does not support that format and requires large
+ buffers to be dequeue, this flag should be enabled to force only linear
+ buffers (see RTE_VHOST_USER_EXTBUF_SUPPORT) or drop the packet.
+
+ It is disabled by default.
+
+ - ``RTE_VHOST_USER_EXTBUF_SUPPORT``
+
+ Enabling this flag allows vhost dequeue function to allocate and attach
+ an external buffer to a pktmbuf if the pkmbuf doesn't provide enough
+ space to store all data.
+
+ This is useful when the vhost application wants to support large packets
+ but doesn't want to increase the default mempool object size nor to
+ support multi-segmented mbufs (non-linear). In this case, a fresh buffer
+ is allocated using rte_malloc() which gets attached to a pktmbuf using
+ rte_pktmbuf_attach_extbuf().
+
+ See RTE_VHOST_USER_LINEARBUF_SUPPORT as well to disable multi-segmented
+ mbufs for application that doesn't support chained mbufs.
+
+ It is disabled by default.
+
* ``rte_vhost_driver_set_features(path, features)``
This function sets the feature bits the vhost-user driver supports. The
diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
index 19474bca0..b821b5df4 100644
--- a/lib/librte_vhost/rte_vhost.h
+++ b/lib/librte_vhost/rte_vhost.h
@@ -30,6 +30,10 @@ extern "C" {
#define RTE_VHOST_USER_DEQUEUE_ZERO_COPY (1ULL << 2)
#define RTE_VHOST_USER_IOMMU_SUPPORT (1ULL << 3)
#define RTE_VHOST_USER_POSTCOPY_SUPPORT (1ULL << 4)
+/* support mbuf with external buffer attached */
+#define RTE_VHOST_USER_EXTBUF_SUPPORT (1ULL << 5)
+/* support only linear buffers (no chained mbufs) */
+#define RTE_VHOST_USER_LINEARBUF_SUPPORT (1ULL << 6)
/** Protocol features. */
#ifndef VHOST_USER_PROTOCOL_F_MQ
diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index 274988c4d..e546be2a8 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -40,6 +40,8 @@ struct vhost_user_socket {
bool dequeue_zero_copy;
bool iommu_support;
bool use_builtin_virtio_net;
+ bool extbuf;
+ bool linearbuf;
/*
* The "supported_features" indicates the feature bits the
@@ -232,6 +234,12 @@ vhost_user_add_connection(int fd, struct vhost_user_socket
*vsocket)
if (vsocket->dequeue_zero_copy)
vhost_enable_dequeue_zero_copy(vid);
+ if (vsocket->extbuf)
+ vhost_enable_extbuf(vid);
+
+ if (vsocket->linearbuf)
+ vhost_enable_linearbuf(vid);
+
RTE_LOG(INFO, VHOST_CONFIG, "new device, handle is %d\n", vid);
if (vsocket->notify_ops->new_connection) {
@@ -870,6 +878,8 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
goto out_free;
}
vsocket->dequeue_zero_copy = flags & RTE_VHOST_USER_DEQUEUE_ZERO_COPY;
+ vsocket->extbuf = flags & RTE_VHOST_USER_EXTBUF_SUPPORT;
+ vsocket->linearbuf = flags & RTE_VHOST_USER_LINEARBUF_SUPPORT;
/*
* Set the supported features correctly for the builtin vhost-user
@@ -894,6 +904,18 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
* not compatible with postcopy.
*/
if (vsocket->dequeue_zero_copy) {
+ if (vsocket->extbuf) {
+ RTE_LOG(ERR, VHOST_CONFIG,
+ "error: zero copy is incompatible with external
buffers\n");
+ ret = -1;
+ goto out_free;
There should be 'out_mutex'.
+ }
+ if (vsocket->linearbuf) {
+ RTE_LOG(ERR, VHOST_CONFIG,
+ "error: zero copy is incompatible with linear
buffers\n");
+ ret = -1;
+ goto out_free;
Ditto.
+ }
vsocket->supported_features &= ~(1ULL << VIRTIO_F_IN_ORDER);
vsocket->features &= ~(1ULL << VIRTIO_F_IN_ORDER);
diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index cea44df8c..77457f538 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -605,6 +605,28 @@ vhost_set_builtin_virtio_net(int vid, bool enable)
dev->flags &= ~VIRTIO_DEV_BUILTIN_VIRTIO_NET;
}
+void
+vhost_enable_extbuf(int vid)
+{
+ struct virtio_net *dev = get_device(vid);
+
+ if (dev == NULL)
+ return;
+
+ dev->extbuf = 1;
+}
+
+void
+vhost_enable_linearbuf(int vid)
+{
+ struct virtio_net *dev = get_device(vid);
+
+ if (dev == NULL)
+ return;
+
+ dev->linearbuf = 1;
+}
+
int
rte_vhost_get_mtu(int vid, uint16_t *mtu)
{
diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 5131a97a3..0346bd118 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -302,6 +302,8 @@ struct virtio_net {
rte_atomic16_t broadcast_rarp;
uint32_t nr_vring;
int dequeue_zero_copy;
+ int extbuf;
+ int linearbuf;
struct vhost_virtqueue *virtqueue[VHOST_MAX_QUEUE_PAIRS * 2];
#define IF_NAME_SZ (PATH_MAX > IFNAMSIZ ? PATH_MAX : IFNAMSIZ)
char ifname[IF_NAME_SZ];
@@ -476,6 +478,8 @@ void vhost_attach_vdpa_device(int vid, int did);
void vhost_set_ifname(int, const char *if_name, unsigned int if_len);
void vhost_enable_dequeue_zero_copy(int vid);
void vhost_set_builtin_virtio_net(int vid, bool enable);
+void vhost_enable_extbuf(int vid);
+void vhost_enable_linearbuf(int vid);
struct vhost_device_ops const *vhost_driver_callback_get(const char *path);
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 5b85b832d..da69ab1db 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -1289,6 +1289,93 @@ get_zmbuf(struct vhost_virtqueue *vq)
return NULL;
}
+static void
+virtio_dev_extbuf_free(void *addr __rte_unused, void *opaque)
+{
+ rte_free(opaque);
+}
+
+static int
+virtio_dev_extbuf_alloc(struct rte_mbuf *pkt, uint32_t size)
+{
+ struct rte_mbuf_ext_shared_info *shinfo = NULL;
+ uint32_t total_len = RTE_PKTMBUF_HEADROOM + size;
+ uint16_t buf_len;
+ rte_iova_t iova;
+ void *buf;
+
+ /* Try to use pkt buffer to store shinfo to reduce the amount of memory
+ * required, otherwise store shinfo in the new buffer.
+ */
+ if (rte_pktmbuf_tailroom(pkt) >= sizeof(*shinfo))
+ shinfo = rte_pktmbuf_mtod(pkt,
+ struct rte_mbuf_ext_shared_info *);
+ else {
+ total_len += sizeof(*shinfo) + sizeof(uintptr_t);
+ total_len = RTE_ALIGN_CEIL(total_len, sizeof(uintptr_t));
+ }
+
+ if (unlikely(total_len > UINT16_MAX))
+ return -ENOSPC;
+
+ buf_len = total_len;
+ buf = rte_malloc(NULL, buf_len, RTE_CACHE_LINE_SIZE);
+ if (unlikely(buf == NULL))
+ return -ENOMEM;
+
+ /* Initialize shinfo */
+ if (shinfo) {
+ shinfo->free_cb = virtio_dev_extbuf_free;
+ shinfo->fcb_opaque = buf;
+ rte_mbuf_ext_refcnt_set(shinfo, 1);
+ } else {
+ shinfo = rte_pktmbuf_ext_shinfo_init_helper(buf, &buf_len,
+ virtio_dev_extbuf_free, buf);
+ if (unlikely(shinfo == NULL)) {
+ rte_free(buf);
+ RTE_LOG(ERR, VHOST_DATA, "Failed to init shinfo\n");
+ return -1;
+ }
+ }
+
+ iova = rte_malloc_virt2iova(buf);
+ rte_pktmbuf_attach_extbuf(pkt, buf, iova, buf_len, shinfo);
+ rte_pktmbuf_reset_headroom(pkt);
+
+ return 0;
+}
+
+/*
+ * Allocate a host supported pktmbuf.
+ */
+static __rte_always_inline struct rte_mbuf *
+virtio_dev_pktmbuf_alloc(struct virtio_net *dev, struct rte_mempool *mp,
+ uint32_t data_len)
+{
+ struct rte_mbuf *pkt = rte_pktmbuf_alloc(mp);
+
+ if (unlikely(pkt == NULL))
+ return NULL;
+
+ if (rte_pktmbuf_tailroom(pkt) >= data_len)
+ return pkt;
+
+ /* attach an external buffer if supported */
+ if (dev->extbuf && !virtio_dev_extbuf_alloc(pkt, data_len))
+ return pkt;
+
+ /* check if chained buffers are allowed */
+ if (!dev->linearbuf)
+ return pkt;
I guess, checking of the 'linearbuf' should go before checking the 'extbuf'.
The usecase is that allocation of several buffers from the memory pool is,
probably, faster than rte_malloc() + memory attaching. So, if the 'linearbuf'
is not requested, it might be faster to use chained mbufs.
BTW, I'm not sure if we really need 2 separate options for this.
i.e. 1. +linear +extbuf --> extbuf allocated
2. +linear -extbuf --> buffer dropped (is this case is useful at all?)
3. -linear +extbuf --> chained mbufs might be preferred (see above)
4. -linear -extbuf --> chained mbufs
Case 4 is a default case. Case 1 is our target case for supporting large
buffers.
Case 3 might makes no much sense as the result is equal to case 4.
Case 2 might be not interesting for as at all, because it will lead to random
packet drops depending on their size.
But, if only cases 1 and 4 are valid and interesting to us, we could easily
merge
both flags.
Thoughts?
