[ovs-dev] [PATCHv3] netdev-afxdp: Add need_wakeup supprt.

Eelco Chaudron echaudro at redhat.com
Tue Sep 17 11:41:17 UTC 2019


Two comments below…
			

On 11 Sep 2019, at 19:58, William Tu wrote:

> 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 at samsung.com>
> Signed-off-by: William Tu <u9012063 at 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(-)
>
> 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.");

This is for compile time only, guess it’s not possible to get this 
runtime, i.e. to see if the kernel supports this?

Guess this related to your comment on the V2:

>> 3) kernel NOT support && libbpf support && user enable
>> —> fails, the AF_XDP packet rx/tx sees no packets (libbpf is not
>> backward compatible?)

> +    }
> +
>      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) {

Maybe move this check to the wakeup_if_needed() function, it’s enabled 
by default so the call should not matter. If libbpf does not support it 
it will be compiled out. What do you think?

> +            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>
> -- 
> 2.7.4


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