[ovs-dev,PATCHv3] netdev-afxdp: Add need_wakeup supprt.
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Message ID 1568224717-97348-1-git-send-email-u9012063@gmail.com
State New
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  • [ovs-dev,PATCHv3] netdev-afxdp: Add need_wakeup supprt.
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Commit Message

William Tu Sept. 11, 2019, 5:58 p.m. UTC
The patch adds support for using need_wakeup flag in AF_XDP rings.
A new option, use_need_wakeup, is added. When this option is used,
it means that OVS has to explicitly wake up the kernel RX, using poll()
syscall and wake up TX, using sendto() syscall. This feature improves
the performance by avoiding unnecessary sendto syscalls for TX.
For RX, instead of kernel always busy-spinning on fille queue, OVS wakes
up the kernel RX processing when fill queue is replenished.

The need_wakeup feature is merged into Linux kernel 5.3.0-rc1 and OVS
enables it by default. Running the feature before this version causes
xsk bind fails, please use options:use_need_wakeup=false to disable it.
If users enable it but runs in an older version of libbpf, then the
need_wakeup feature has no effect, and a warning message is logged.

For virtual interface, it's better set use_need_wakeup=false, since
the virtual device's AF_XDP xmit is synchronous: the sendto syscall
enters kernel and process the TX packet on tx queue directly.

I tested on kernel 5.3.0-rc3 using its libbpf.  On Intel Xeon E5-2620
v3 2.4GHz system, performance of physical port to physical port improves
from 6.1Mpps to 7.3Mpps. Testing on 5.2.0-rc6 using libbpf from 5.3.0-rc3
does not work due to libbpf API change. Users have to use the older
libbpf for older kernel.

Suggested-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: William Tu <u9012063@gmail.com>
---
v3:
- add warning when user enables it but libbpf not support it
- revise documentation

v2:
- address feedbacks from Ilya and Eelco
- add options:use_need_wakeup, default to true
- remove poll timeout=1sec, make poll() return immediately
- naming change: rename to xsk_rx_wakeup_if_needing
- fix indents and return value for errno
---
 Documentation/intro/install/afxdp.rst |  15 ++++-
 acinclude.m4                          |   8 +++
 lib/netdev-afxdp.c                    | 101 ++++++++++++++++++++++++++++++----
 lib/netdev-linux-private.h            |   2 +
 vswitchd/vswitch.xml                  |  13 +++++
 5 files changed, 124 insertions(+), 15 deletions(-)

Patch
diff mbox series

diff --git a/Documentation/intro/install/afxdp.rst b/Documentation/intro/install/afxdp.rst
index 820e9d993d8f..545516b2bbec 100644
--- a/Documentation/intro/install/afxdp.rst
+++ b/Documentation/intro/install/afxdp.rst
@@ -176,9 +176,18 @@  in :doc:`general`::
   ovs-vswitchd ...
   ovs-vsctl -- add-br br0 -- set Bridge br0 datapath_type=netdev
 
-Make sure your device driver support AF_XDP, and to use 1 PMD (on core 4)
-on 1 queue (queue 0) device, configure these options: **pmd-cpu-mask,
-pmd-rxq-affinity, and n_rxq**. The **xdpmode** can be "drv" or "skb"::
+Make sure your device driver support AF_XDP, netdev-afxdp supports
+the following additional options (see man ovs-vswitchd.conf.db for
+more details):
+
+ * **xdpmode**: use "drv" for driver mode, or "skb" for skb mode.
+
+ * **use_need_wakeup**: disable by setting to "false", otherwise default
+   is "true"
+
+For example, to use 1 PMD (on core 4) on 1 queue (queue 0) device,
+configure these options: **pmd-cpu-mask, pmd-rxq-affinity, and n_rxq**.
+The **xdpmode** can be "drv" or "skb"::
 
   ethtool -L enp2s0 combined 1
   ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=0x10
diff --git a/acinclude.m4 b/acinclude.m4
index f0e38898b17a..df1082c455fc 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -276,6 +276,14 @@  AC_DEFUN([OVS_CHECK_LINUX_AF_XDP], [
               [Define to 1 if AF_XDP support is available and enabled.])
     LIBBPF_LDADD=" -lbpf -lelf"
     AC_SUBST([LIBBPF_LDADD])
+
+    AC_CHECK_DECL([xsk_ring_prod__needs_wakeup], [
+      AC_DEFINE([HAVE_XDP_NEED_WAKEUP], [1],
+        [XDP need wakeup support detected in xsk.h.])
+    ], [
+      AC_DEFINE([HAVE_XDP_NEED_WAKEUP], [0],
+        [XDP need wakeup support not detected in xsk.h.])
+      ], [#include <bpf/xsk.h>])
   fi
   AM_CONDITIONAL([HAVE_AF_XDP], test "$AF_XDP_ENABLE" = true)
 ])
diff --git a/lib/netdev-afxdp.c b/lib/netdev-afxdp.c
index e5b058d08a09..4d4c90f91806 100644
--- a/lib/netdev-afxdp.c
+++ b/lib/netdev-afxdp.c
@@ -26,6 +26,7 @@ 
 #include <linux/rtnetlink.h>
 #include <linux/if_xdp.h>
 #include <net/if.h>
+#include <poll.h>
 #include <stdlib.h>
 #include <sys/resource.h>
 #include <sys/socket.h>
@@ -82,7 +83,7 @@  BUILD_ASSERT_DECL(PROD_NUM_DESCS == CONS_NUM_DESCS);
 #define UMEM2DESC(elem, base) ((uint64_t)((char *)elem - (char *)base))
 
 static struct xsk_socket_info *xsk_configure(int ifindex, int xdp_queue_id,
-                                             int mode);
+                                             int mode, bool use_need_wakeup);
 static void xsk_remove_xdp_program(uint32_t ifindex, int xdpmode);
 static void xsk_destroy(struct xsk_socket_info *xsk);
 static int xsk_configure_all(struct netdev *netdev);
@@ -117,6 +118,49 @@  struct xsk_socket_info {
     atomic_uint64_t tx_dropped;
 };
 
+#ifdef HAVE_XDP_NEED_WAKEUP
+static inline void
+xsk_rx_wakeup_if_needed(struct xsk_umem_info *umem,
+                        struct netdev *netdev, int fd)
+{
+    struct pollfd pfd;
+    int ret;
+
+    if (xsk_ring_prod__needs_wakeup(&umem->fq)) {
+        pfd.fd = fd;
+        pfd.events = POLLIN;
+
+        ret = poll(&pfd, 1, 0);
+        if (OVS_UNLIKELY(ret < 0)) {
+            VLOG_WARN_RL(&rl, "%s: error polling rx fd: %s.",
+                         netdev_get_name(netdev),
+                         ovs_strerror(errno));
+        }
+    }
+}
+
+static inline bool
+xsk_tx_need_wakeup(struct xsk_socket_info *xsk_info)
+{
+    return xsk_ring_prod__needs_wakeup(&xsk_info->tx);
+}
+
+#else /* !HAVE_XDP_NEED_WAKEUP */
+static inline void
+xsk_rx_wakeup_if_needed(struct xsk_umem_info *umem OVS_UNUSED,
+                        struct netdev *netdev OVS_UNUSED,
+                        int fd OVS_UNUSED)
+{
+    /* Nothing. */
+}
+
+static inline bool
+xsk_tx_need_wakeup(struct xsk_socket_info *xsk_info OVS_UNUSED)
+{
+    return true;
+}
+#endif /* HAVE_XDP_NEED_WAKEUP */
+
 static void
 netdev_afxdp_cleanup_unused_pool(struct unused_pool *pool)
 {
@@ -234,7 +278,7 @@  xsk_configure_umem(void *buffer, uint64_t size, int xdpmode)
 
 static struct xsk_socket_info *
 xsk_configure_socket(struct xsk_umem_info *umem, uint32_t ifindex,
-                     uint32_t queue_id, int xdpmode)
+                     uint32_t queue_id, int xdpmode, bool use_need_wakeup)
 {
     struct xsk_socket_config cfg;
     struct xsk_socket_info *xsk;
@@ -257,6 +301,12 @@  xsk_configure_socket(struct xsk_umem_info *umem, uint32_t ifindex,
         cfg.xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST | XDP_FLAGS_SKB_MODE;
     }
 
+    if (use_need_wakeup) {
+#ifdef HAVE_XDP_NEED_WAKEUP
+        cfg.bind_flags |= XDP_USE_NEED_WAKEUP;
+#endif
+    }
+
     if (if_indextoname(ifindex, devname) == NULL) {
         VLOG_ERR("ifindex %d to devname failed (%s)",
                  ifindex, ovs_strerror(errno));
@@ -267,9 +317,11 @@  xsk_configure_socket(struct xsk_umem_info *umem, uint32_t ifindex,
     ret = xsk_socket__create(&xsk->xsk, devname, queue_id, umem->umem,
                              &xsk->rx, &xsk->tx, &cfg);
     if (ret) {
-        VLOG_ERR("xsk_socket__create failed (%s) mode: %s qid: %d",
+        VLOG_ERR("xsk_socket__create failed (%s) mode: %s "
+                 "use_need_wakeup: %s qid: %d",
                  ovs_strerror(errno),
                  xdpmode == XDP_COPY ? "SKB": "DRV",
+                 use_need_wakeup ? "true" : "false",
                  queue_id);
         free(xsk);
         return NULL;
@@ -311,7 +363,8 @@  xsk_configure_socket(struct xsk_umem_info *umem, uint32_t ifindex,
 }
 
 static struct xsk_socket_info *
-xsk_configure(int ifindex, int xdp_queue_id, int xdpmode)
+xsk_configure(int ifindex, int xdp_queue_id, int xdpmode,
+              bool use_need_wakeup)
 {
     struct xsk_socket_info *xsk;
     struct xsk_umem_info *umem;
@@ -334,7 +387,8 @@  xsk_configure(int ifindex, int xdp_queue_id, int xdpmode)
 
     VLOG_DBG("Allocated umem pool at 0x%"PRIxPTR, (uintptr_t) umem);
 
-    xsk = xsk_configure_socket(umem, ifindex, xdp_queue_id, xdpmode);
+    xsk = xsk_configure_socket(umem, ifindex, xdp_queue_id, xdpmode,
+                               use_need_wakeup);
     if (!xsk) {
         /* Clean up umem and xpacket pool. */
         if (xsk_umem__delete(umem->umem)) {
@@ -365,9 +419,12 @@  xsk_configure_all(struct netdev *netdev)
 
     /* Configure each queue. */
     for (i = 0; i < n_rxq; i++) {
-        VLOG_INFO("%s: configure queue %d mode %s", __func__, i,
-                  dev->xdpmode == XDP_COPY ? "SKB" : "DRV");
-        xsk_info = xsk_configure(ifindex, i, dev->xdpmode);
+        VLOG_INFO("%s: configure queue %d mode %s use_need_wakeup %s.",
+                  __func__, i,
+                  dev->xdpmode == XDP_COPY ? "SKB" : "DRV",
+                  dev->use_need_wakeup ? "true" : "false");
+        xsk_info = xsk_configure(ifindex, i, dev->xdpmode,
+                                 dev->use_need_wakeup);
         if (!xsk_info) {
             VLOG_ERR("Failed to create AF_XDP socket on queue %d.", i);
             dev->xsks[i] = NULL;
@@ -459,6 +516,7 @@  netdev_afxdp_set_config(struct netdev *netdev, const struct smap *args,
     struct netdev_linux *dev = netdev_linux_cast(netdev);
     const char *str_xdpmode;
     int xdpmode, new_n_rxq;
+    bool need_wakeup;
 
     ovs_mutex_lock(&dev->mutex);
     new_n_rxq = MAX(smap_get_int(args, "n_rxq", NR_QUEUE), 1);
@@ -481,10 +539,17 @@  netdev_afxdp_set_config(struct netdev *netdev, const struct smap *args,
         return EINVAL;
     }
 
+    need_wakeup = smap_get_bool(args, "use_need_wakeup", true);
+    if (need_wakeup && !HAVE_XDP_NEED_WAKEUP) {
+        VLOG_WARN("XDP need_wakeup is not supported in libbpf.");
+    }
+
     if (dev->requested_n_rxq != new_n_rxq
-        || dev->requested_xdpmode != xdpmode) {
+        || dev->requested_xdpmode != xdpmode
+        || dev->requested_need_wakeup != need_wakeup) {
         dev->requested_n_rxq = new_n_rxq;
         dev->requested_xdpmode = xdpmode;
+        dev->requested_need_wakeup = need_wakeup;
         netdev_request_reconfigure(netdev);
     }
     ovs_mutex_unlock(&dev->mutex);
@@ -500,6 +565,8 @@  netdev_afxdp_get_config(const struct netdev *netdev, struct smap *args)
     smap_add_format(args, "n_rxq", "%d", netdev->n_rxq);
     smap_add_format(args, "xdpmode", "%s",
         dev->xdpmode == XDP_ZEROCOPY ? "drv" : "skb");
+    smap_add_format(args, "use_need_wakeup", "%s",
+        dev->use_need_wakeup ? "true" : "false");
     ovs_mutex_unlock(&dev->mutex);
     return 0;
 }
@@ -515,6 +582,7 @@  netdev_afxdp_reconfigure(struct netdev *netdev)
 
     if (netdev->n_rxq == dev->requested_n_rxq
         && dev->xdpmode == dev->requested_xdpmode
+        && dev->use_need_wakeup == dev->requested_need_wakeup
         && dev->xsks) {
         goto out;
     }
@@ -538,6 +606,7 @@  netdev_afxdp_reconfigure(struct netdev *netdev)
          * when no device is in DRV mode.
          */
     }
+    dev->use_need_wakeup = dev->requested_need_wakeup;
 
     err = xsk_configure_all(netdev);
     if (err) {
@@ -660,6 +729,9 @@  netdev_afxdp_rxq_recv(struct netdev_rxq *rxq_, struct dp_packet_batch *batch,
 
     rcvd = xsk_ring_cons__peek(&xsk_info->rx, BATCH_SIZE, &idx_rx);
     if (!rcvd) {
+        if (dev->use_need_wakeup) {
+            xsk_rx_wakeup_if_needed(umem, netdev, rx->fd);
+        }
         return EAGAIN;
     }
 
@@ -704,11 +776,15 @@  netdev_afxdp_rxq_recv(struct netdev_rxq *rxq_, struct dp_packet_batch *batch,
 }
 
 static inline int
-kick_tx(struct xsk_socket_info *xsk_info, int xdpmode)
+kick_tx(struct xsk_socket_info *xsk_info, int xdpmode, bool use_need_wakeup)
 {
     int ret, retries;
     static const int KERNEL_TX_BATCH_SIZE = 16;
 
+    if (use_need_wakeup && !xsk_tx_need_wakeup(xsk_info)) {
+        return 0;
+    }
+
     /* In SKB_MODE packet transmission is synchronous, and the kernel xmits
      * only TX_BATCH_SIZE(16) packets for a single sendmsg syscall.
      * So, we have to kick the kernel (n_packets / 16) times to be sure that
@@ -876,7 +952,7 @@  __netdev_afxdp_batch_send(struct netdev *netdev, int qid,
         atomic_add_relaxed(&xsk_info->tx_dropped, batch->count, &orig);
         COVERAGE_INC(afxdp_tx_full);
         afxdp_complete_tx(xsk_info);
-        kick_tx(xsk_info, dev->xdpmode);
+        kick_tx(xsk_info, dev->xdpmode, dev->use_need_wakeup);
         error = ENOMEM;
         goto out;
     }
@@ -900,7 +976,7 @@  __netdev_afxdp_batch_send(struct netdev *netdev, int qid,
     xsk_ring_prod__submit(&xsk_info->tx, batch->count);
     xsk_info->outstanding_tx += batch->count;
 
-    ret = kick_tx(xsk_info, dev->xdpmode);
+    ret = kick_tx(xsk_info, dev->xdpmode, dev->use_need_wakeup);
     if (OVS_UNLIKELY(ret)) {
         VLOG_WARN_RL(&rl, "%s: error sending AF_XDP packet: %s.",
                      netdev_get_name(netdev), ovs_strerror(ret));
@@ -970,6 +1046,7 @@  netdev_afxdp_construct(struct netdev *netdev)
 
     dev->requested_n_rxq = NR_QUEUE;
     dev->requested_xdpmode = XDP_COPY;
+    dev->requested_need_wakeup = true;
 
     dev->xsks = NULL;
     dev->tx_locks = NULL;
diff --git a/lib/netdev-linux-private.h b/lib/netdev-linux-private.h
index a350be151147..c14f2fb81bb0 100644
--- a/lib/netdev-linux-private.h
+++ b/lib/netdev-linux-private.h
@@ -102,6 +102,8 @@  struct netdev_linux {
     int requested_n_rxq;
     int xdpmode;                /* AF_XDP running mode: driver or skb. */
     int requested_xdpmode;
+    bool use_need_wakeup;
+    bool requested_need_wakeup;
     struct ovs_spin *tx_locks;  /* spin lock array for TX queues. */
 #endif
 };
diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index 9a743c05b4bf..e8b428d323c7 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -3147,6 +3147,19 @@  ovs-vsctl add-port br0 p0 -- set Interface p0 type=patch options:peer=p1 \
         </p>
       </column>
 
+      <column name="options" key="use_need_wakeup"
+              type='{"type": "boolean"}'>
+        <p>
+          Specifies whether to use need_wakeup feature in afxdp netdev.
+          (required kernel version later than 5.3.0-rc1)
+          If enabled, OVS explicitly wakes up the kernel RX, using poll()
+          syscall and wakes up TX, using sendto() syscall. For physical
+          devices, this feature improves the performance by avoiding
+          unnecessary sendto syscalls.
+          Defaults is true.
+        </p>
+      </column>
+
       <column name="options" key="vhost-server-path"
               type='{"type": "string"}'>
         <p>