[ovs-dev] [PATCH v8] dpif-netlink: distribute polling to discreet handlers

Ilya Maximets i.maximets at ovn.org
Thu Sep 17 18:43:38 UTC 2020


On 9/9/20 7:08 PM, Mark Gray wrote:
> From: Aaron Conole <aconole at redhat.com>
> 
> Currently, the channel handlers are polled globally.  On some
> systems, this causes a thundering herd issue where multiple
> handler threads become active, only to do no work and immediately
> sleep.
> 
> The approach here is to push the netlink socket channels to discreet
> handler threads to process, rather than polling on every thread.
> This will eliminate the need to wake multiple threads.
> 
> To check:
> 
>   ip netns add left
>   ip netns add right
>   ip link add center-left type veth peer name left0 netns left
>   ip link add center-right type veth peer name right0 netns right
>   ip link set center-left up
>   ip link set center-right up
>   ip -n left ip link set left0 up
>   ip -n left ip addr add 172.31.110.10/24 dev left0
>   ip -n right ip link set right0 up
>   ip -n right ip addr add 172.31.110.11/24 dev right0
> 
>   ovs-vsctl add-br br0
>   ovs-vsctl add-port br0 center-right
>   ovs-vsctl add-port br0 center-left
> 
>   # in one terminal
>   perf record -e sched:sched_wakeup,irq:softirq_entry -ag
> 
>   # in a separate terminal
>   ip netns exec left arping -I left0 -c 1 172.31.110.11
> 
>   # in the perf terminal after exiting
>   perf script
> 
> Look for the number of 'handler' threads which were made active.
> 
> Suggested-by: Ben Pfaff <blp at ovn.org>
> Co-authored-by: Mark Gray <mark.d.gray at redhat.com>
> Reported-by: David Ahern <dsahern at gmail.com>
> Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2019-December/365857.html
> Cc: Matteo Croce <technoboy85 at gmail.com>
> Cc: Flavio Leitner <fbl at sysclose.org>
> Fixes: 69c51582f ("dpif-netlink: don't allocate per thread netlink sockets")
> Signed-off-by: Aaron Conole <aconole at redhat.com>
> Signed-off-by: Mark Gray <mark.d.gray at redhat.com>
> ---
> 
> 
> v2: Oops - forgot to commit my whitespace cleanups.
> v3: one port latency results as per Matteo's comments
> 
>     Stock:
>       min/avg/max/mdev = 21.5/36.5/96.5/1.0 us
>     With Patch:
>       min/avg/max/mdev = 5.3/9.7/98.4/0.5 us 
> v4: Oops - first email did not send
> v5:   min/avg/max/mdev = 9.3/10.4/33.6/2.2 us
> v6: Split out the AUTHORS patch and added a cover letter as
>     per Ilya's suggestion.
>     Fixed 0-day issues.
> v7: Merged patches as per Flavio's suggestion. This is
>     no longer a series. Fixed some other small issues.
> 
>  lib/dpif-netlink.c | 330 +++++++++++++++++++++++++--------------------
>  lib/id-pool.c      |  10 ++
>  lib/id-pool.h      |   1 +
>  3 files changed, 197 insertions(+), 144 deletions(-)
> 
> diff --git a/lib/dpif-netlink.c b/lib/dpif-netlink.c
> index 7da4fb54d..a74838506 100644
> --- a/lib/dpif-netlink.c
> +++ b/lib/dpif-netlink.c
> @@ -37,6 +37,7 @@
>  #include "dpif-provider.h"
>  #include "fat-rwlock.h"
>  #include "flow.h"
> +#include "id-pool.h"
>  #include "netdev-linux.h"
>  #include "netdev-offload.h"
>  #include "netdev-provider.h"
> @@ -160,6 +161,9 @@ static void dpif_netlink_flow_to_dpif_flow(struct dpif_flow *,
>  
>  /* One of the dpif channels between the kernel and userspace. */
>  struct dpif_channel {
> +    struct hmap_node hmap_node;

This needs a comment and all other new structure fileds too.
Ex.:
    struct hmap_node hmap_node; /* In struct dpif_handler's channels hmap. */

> +    struct dpif_handler *handler;

Why do we need this back-pointer?  Maybe it's better to just add 'handler'
argument to dpif_channel_del() ?

> +    uint32_t port_idx;

I see a lot of 'port_idx' here and there, but it's not really an index anymore.
You removed all the arrays that used these variables as index.
Can we just use 'port_no' directly here?  I know that there will be conversions
from odp to u32, but this should be more clear.  If conversions are the issue,
we could store u32 version of 'port_no' here.

And, please, add a comment.

>      struct nl_sock *sock;       /* Netlink socket. */
>      long long int last_poll;    /* Last time this channel was polled. */
>  };
> @@ -183,6 +187,8 @@ struct dpif_handler {
>      int n_events;                 /* Num events returned by epoll_wait(). */
>      int event_offset;             /* Offset into 'epoll_events'. */
>  
> +    struct hmap channels;         /* map of channels for each port. */

Comment style: Capital letter.

> +
>  #ifdef _WIN32
>      /* Pool of sockets. */
>      struct dpif_windows_vport_sock *vport_sock_pool;
> @@ -201,9 +207,8 @@ struct dpif_netlink {
>      struct fat_rwlock upcall_lock;
>      struct dpif_handler *handlers;
>      uint32_t n_handlers;           /* Num of upcall handlers. */
> -    struct dpif_channel *channels; /* Array of channels for each port. */
> -    int uc_array_size;             /* Size of 'handler->channels' and */
> -                                   /* 'handler->epoll_events'. */
> +
> +    struct id_pool *port_ids;      /* Set of added port ids */

What is the reason of having this pool?  Datapath port numbers are unique
except for ODPP_NONE, and all the functions you implemented actually
iterates over all channels anyway to find one with requested port_idx.
So, the only purpose of it is to avoid searching on incorect port number,
but this should be a rare case.  Can we just remove it?

OTOH, if it's necessary to have this id pool, I'd suggest to use hmapx
instead as it already has all required infrastructure and doesn't actually
care about range of values.

>  
>      /* Change notification. */
>      struct nl_sock *port_notifier; /* vport multicast group subscriber. */
> @@ -287,6 +292,44 @@ close_nl_sock(struct nl_sock *sock)
>  #endif
>  }
>  
> +static size_t
> +dpif_handler_channels_count(const struct dpif_handler *handler)
> +{
> +    return hmap_count(&handler->channels);
> +}
> +
> +static struct dpif_channel *
> +dpif_handler_channel_find(struct dpif_handler *handler, uint32_t idx)
> +{
> +    struct dpif_channel *channel;
> +
> +    HMAP_FOR_EACH_WITH_HASH (channel, hmap_node, hash_int(idx, 0),
> +                             &handler->channels) {
> +        if (channel->port_idx == idx) {
> +            return channel;
> +        }
> +    }
> +
> +    return NULL;
> +}
> +
> +static void
> +dpif_channel_del(struct dpif_netlink *dpif,
> +                 struct dpif_channel *channel)

As suggested above, it might make sense to just pass 'handler' here and
avoid having back-pointer inside the channel structure.

> +{
> +    struct dpif_handler *handler = channel->handler;
> +
> +#ifndef _WIN32
> +    epoll_ctl(handler->epoll_fd, EPOLL_CTL_DEL,
> +              nl_sock_fd(channel->sock), NULL);
> +    nl_sock_destroy(channel->sock);
> +#endif
> +    hmap_remove(&handler->channels, &channel->hmap_node);
> +    id_pool_free_id(dpif->port_ids, channel->port_idx);
> +    handler->event_offset = handler->n_events = 0;
> +    free(channel);
> +}
> +
>  static struct dpif_netlink *
>  dpif_netlink_cast(const struct dpif *dpif)
>  {
> @@ -385,6 +428,7 @@ open_dpif(const struct dpif_netlink_dp *dp, struct dpif **dpifp)
>  
>      dpif->dp_ifindex = dp->dp_ifindex;
>      dpif->user_features = dp->user_features;
> +    dpif->port_ids = id_pool_create(0, MAX_PORTS);
>      *dpifp = &dpif->dpif;
>  
>      return 0;
> @@ -446,167 +490,151 @@ error:
>  }
>  #endif /* _WIN32 */
>  
> -/* Given the port number 'port_idx', extracts the pid of netlink socket
> +/* Given the port number 'port_no', extracts the pid of netlink socket
>   * associated to the port and assigns it to 'upcall_pid'. */
>  static bool
> -vport_get_pid(struct dpif_netlink *dpif, uint32_t port_idx,
> +vport_get_pid(struct dpif_netlink *dpif, odp_port_t port_no,
>                uint32_t *upcall_pid)

This function seems redundant as it does almost same thing as
dpif_netlink_port_get_pid__().  Can we combine them?

>  {
> -    /* Since the nl_sock can only be assigned in either all
> -     * or none "dpif" channels, the following check
> -     * would suffice. */
> -    if (!dpif->channels[port_idx].sock) {
> +    uint32_t port_idx = odp_to_u32(port_no);
> +    size_t i;
> +
> +    ovs_assert(!WINDOWS || dpif->n_handlers <= 1);
> +
> +    if (!id_pool_has_id(dpif->port_ids, port_idx)) {
>          return false;
>      }
> -    ovs_assert(!WINDOWS || dpif->n_handlers <= 1);
>  
> -    *upcall_pid = nl_sock_pid(dpif->channels[port_idx].sock);
> +    /* The 'port_idx' should only be valid for a single handler. */
> +    for (i = 0; i < dpif->n_handlers; i++) {
> +        struct dpif_channel *channel;
> +
> +        channel = dpif_handler_channel_find(&dpif->handlers[i], port_idx);
> +        if (channel) {
> +            *upcall_pid = nl_sock_pid(channel->sock);
> +            return true;
> +        }
> +    }
>  
> -    return true;
> +    return false;
>  }
>  
>  static int
>  vport_add_channel(struct dpif_netlink *dpif, odp_port_t port_no,
>                    struct nl_sock *sock)
>  {
> -    struct epoll_event event;
>      uint32_t port_idx = odp_to_u32(port_no);
> +    struct dpif_channel *channel;
> +    struct dpif_handler *handler;
> +    struct epoll_event event;
>      size_t i;
> -    int error;
>  
> -    if (dpif->handlers == NULL) {
> +    if (dpif->handlers == NULL ||
> +        id_pool_has_id(dpif->port_ids, port_idx)) {
>          close_nl_sock(sock);
> -        return 0;
> +        return EINVAL;
>      }
>  
> -    /* We assume that the datapath densely chooses port numbers, which can
> -     * therefore be used as an index into 'channels' and 'epoll_events' of
> -     * 'dpif'. */
> -    if (port_idx >= dpif->uc_array_size) {
> -        uint32_t new_size = port_idx + 1;
> -
> -        if (new_size > MAX_PORTS) {
> -            VLOG_WARN_RL(&error_rl, "%s: datapath port %"PRIu32" too big",
> -                         dpif_name(&dpif->dpif), port_no);
> -            return EFBIG;
> -        }
> +    if (port_idx >= MAX_PORTS) {
> +        VLOG_WARN_RL(&error_rl, "%s: datapath port %"PRIu32" too big",
> +                     dpif_name(&dpif->dpif), port_no);

This looks a bit wierd since we're checking port_idx and printing port_no
instead.  Might be refined if we will just use port_no everywhere.

> +        return EFBIG;
> +    }
>  
> -        dpif->channels = xrealloc(dpif->channels,
> -                                  new_size * sizeof *dpif->channels);
> +    handler = &dpif->handlers[0];
>  
> -        for (i = dpif->uc_array_size; i < new_size; i++) {
> -            dpif->channels[i].sock = NULL;
> +    for (i = 0; i < dpif->n_handlers; i++) {
> +        if (dpif_handler_channels_count(&dpif->handlers[i]) <
> +            dpif_handler_channels_count(handler)) {
> +            handler = &dpif->handlers[i];
>          }
> +    }
>  
> -        for (i = 0; i < dpif->n_handlers; i++) {
> -            struct dpif_handler *handler = &dpif->handlers[i];
> +    channel = xmalloc(sizeof *channel);
> +    channel->port_idx = port_idx;
> +    channel->sock = sock;
> +    channel->last_poll = LLONG_MIN;
> +    channel->handler = handler;
> +    hmap_insert(&handler->channels, &channel->hmap_node,
> +                hash_int(port_idx, 0));
>  
> -            handler->epoll_events = xrealloc(handler->epoll_events,
> -                new_size * sizeof *handler->epoll_events);
> -
> -        }
> -        dpif->uc_array_size = new_size;
> -    }
> +    handler->epoll_events = xrealloc(handler->epoll_events,
> +                                     dpif_handler_channels_count(handler) *
> +                                     sizeof *handler->epoll_events);
>  
>      memset(&event, 0, sizeof event);
>      event.events = EPOLLIN | EPOLLEXCLUSIVE;
>      event.data.u32 = port_idx;
>  
> -    for (i = 0; i < dpif->n_handlers; i++) {
> -        struct dpif_handler *handler = &dpif->handlers[i];
> -
>  #ifndef _WIN32
> -        if (epoll_ctl(handler->epoll_fd, EPOLL_CTL_ADD, nl_sock_fd(sock),
> -                      &event) < 0) {
> -            error = errno;
> -            goto error;
> -        }
> -#endif
> -    }
> -    dpif->channels[port_idx].sock = sock;
> -    dpif->channels[port_idx].last_poll = LLONG_MIN;
> -
> -    return 0;
> -
> -error:
> -#ifndef _WIN32
> -    while (i--) {
> -        epoll_ctl(dpif->handlers[i].epoll_fd, EPOLL_CTL_DEL,
> -                  nl_sock_fd(sock), NULL);
> +    if (epoll_ctl(handler->epoll_fd, EPOLL_CTL_ADD, nl_sock_fd(sock),
> +                  &event) < 0) {
> +        hmap_remove(&handler->channels, &channel->hmap_node);
> +        free(channel);
> +        id_pool_free_id(dpif->port_ids, port_idx);
> +        return errno;
>      }
>  #endif
> -    dpif->channels[port_idx].sock = NULL;
>  
> -    return error;
> +    id_pool_add(dpif->port_ids, port_idx);
> +    return 0;
>  }
>  
> -static void
> -vport_del_channels(struct dpif_netlink *dpif, odp_port_t port_no)
> +static bool
> +vport_del_channel(struct dpif_netlink *dpif, odp_port_t port_no)
>  {
> -    uint32_t port_idx = odp_to_u32(port_no);
>      size_t i;
>  
> -    if (!dpif->handlers || port_idx >= dpif->uc_array_size
> -        || !dpif->channels[port_idx].sock) {
> -        return;
> -    }
> -
>      for (i = 0; i < dpif->n_handlers; i++) {
> -        struct dpif_handler *handler = &dpif->handlers[i];
> -#ifndef _WIN32
> -        epoll_ctl(handler->epoll_fd, EPOLL_CTL_DEL,
> -                  nl_sock_fd(dpif->channels[port_idx].sock), NULL);
> -#endif
> -        handler->event_offset = handler->n_events = 0;
> +        struct dpif_channel *channel;
> +
> +        channel = dpif_handler_channel_find(&dpif->handlers[i],
> +                                            odp_to_u32(port_no));
> +        if (channel) {
> +            dpif_channel_del(dpif, channel);
> +            return true;
> +        }
>      }
> -#ifndef _WIN32
> -    nl_sock_destroy(dpif->channels[port_idx].sock);
> -#endif
> -    dpif->channels[port_idx].sock = NULL;
> +
> +    return false;
>  }
>  
>  static void
>  destroy_all_channels(struct dpif_netlink *dpif)
>      OVS_REQ_WRLOCK(dpif->upcall_lock)
>  {
> -    unsigned int i;
> +    size_t i;
>  
>      if (!dpif->handlers) {
>          return;
>      }
>  
> -    for (i = 0; i < dpif->uc_array_size; i++ ) {
> -        struct dpif_netlink_vport vport_request;
> -        uint32_t upcall_pids = 0;
> -
> -        if (!dpif->channels[i].sock) {
> -            continue;
> -        }
> -
> -        /* Turn off upcalls. */
> -        dpif_netlink_vport_init(&vport_request);
> -        vport_request.cmd = OVS_VPORT_CMD_SET;
> -        vport_request.dp_ifindex = dpif->dp_ifindex;
> -        vport_request.port_no = u32_to_odp(i);
> -        vport_request.n_upcall_pids = 1;
> -        vport_request.upcall_pids = &upcall_pids;
> -        dpif_netlink_vport_transact(&vport_request, NULL, NULL);
> -
> -        vport_del_channels(dpif, u32_to_odp(i));
> -    }
> -
>      for (i = 0; i < dpif->n_handlers; i++) {
>          struct dpif_handler *handler = &dpif->handlers[i];
> +        struct dpif_channel *channel, *next;
> +
> +        HMAP_FOR_EACH_SAFE (channel, next, hmap_node, &handler->channels) {
> +            struct dpif_netlink_vport vport_request;
> +            uint32_t upcall_pids = 0;

Empty line, please.

> +            /* Turn off upcalls. */
> +            dpif_netlink_vport_init(&vport_request);
> +            vport_request.cmd = OVS_VPORT_CMD_SET;
> +            vport_request.dp_ifindex = dpif->dp_ifindex;
> +            vport_request.port_no = u32_to_odp(channel->port_idx);
> +            vport_request.n_upcall_pids = 1;
> +            vport_request.upcall_pids = &upcall_pids;
> +            dpif_netlink_vport_transact(&vport_request, NULL, NULL);
> +            ovs_assert(channel != NULL);
> +            dpif_channel_del(dpif, channel);
> +        }
>  
>          dpif_netlink_handler_uninit(handler);
>          free(handler->epoll_events);
>      }
> -    free(dpif->channels);
> +
>      free(dpif->handlers);
>      dpif->handlers = NULL;
> -    dpif->channels = NULL;
>      dpif->n_handlers = 0;
> -    dpif->uc_array_size = 0;
>  }
>  
>  static void
> @@ -618,9 +646,11 @@ dpif_netlink_close(struct dpif *dpif_)
>  
>      fat_rwlock_wrlock(&dpif->upcall_lock);
>      destroy_all_channels(dpif);
> +    id_pool_destroy(dpif->port_ids);
>      fat_rwlock_unlock(&dpif->upcall_lock);
>  
>      fat_rwlock_destroy(&dpif->upcall_lock);
> +
>      free(dpif);
>  }
>  
> @@ -1003,7 +1033,9 @@ dpif_netlink_port_del__(struct dpif_netlink *dpif, odp_port_t port_no)
>  #endif
>      error = dpif_netlink_vport_transact(&vport, NULL, NULL);
>  
> -    vport_del_channels(dpif, port_no);
> +    if (!vport_del_channel(dpif, port_no)) {

If packets receiving disabled with dpif_recv_set(), there will be no channels
and this check will fail.  And if it we will return here we will leave tunnel
port in a system which is not a good thing.

And we will also leak 'dpif_port' here.

> +        return EINVAL;
> +    }
>  
>      if (!error && !ovs_tunnels_out_of_tree) {
>          error = dpif_netlink_rtnl_port_destroy(dpif_port.name, dpif_port.type);
> @@ -1084,23 +1116,39 @@ dpif_netlink_port_get_pid__(const struct dpif_netlink *dpif,
>                              odp_port_t port_no)
>      OVS_REQ_RDLOCK(dpif->upcall_lock)
>  {
> +    struct dpif_channel *min_channel = NULL, *found_channel = NULL;
>      uint32_t port_idx = odp_to_u32(port_no);
>      uint32_t pid = 0;
> +    size_t i;
> +
> +    /* The ODPP_NONE "reserved" port number uses the "ovs-system"'s
> +     * channel, since it is not heavily loaded. */
> +    uint32_t idx = port_no == ODPP_NONE ? 0 : port_idx;
> +
> +    if (!id_pool_has_id(dpif->port_ids, port_idx)) {
> +        return 0;
> +    }
> +
> +    if (dpif->handlers) {
> +        for (i = 0; i < dpif->n_handlers; i++) {
> +            if (dpif_handler_channel_find(&dpif->handlers[i], idx)) {
> +                found_channel = dpif_handler_channel_find(&dpif->handlers[i],
> +                                                          idx);

Looking up twice seems inefficient.  Same for the 0 case below.

> +                break;
> +            }
>  
> -    if (dpif->handlers && dpif->uc_array_size > 0) {
> -        /* The ODPP_NONE "reserved" port number uses the "ovs-system"'s
> -         * channel, since it is not heavily loaded. */
> -        uint32_t idx = port_idx >= dpif->uc_array_size ? 0 : port_idx;
> -
> -        /* Needs to check in case the socket pointer is changed in between
> -         * the holding of upcall_lock.  A known case happens when the main
> -         * thread deletes the vport while the handler thread is handling
> -         * the upcall from that port. */
> -        if (dpif->channels[idx].sock) {
> -            pid = nl_sock_pid(dpif->channels[idx].sock);
> +            if (dpif_handler_channel_find(&dpif->handlers[i], 0)) {
> +                min_channel = dpif_handler_channel_find(&dpif->handlers[i], 0);
> +            }
>          }
>      }
>  
> +    if (found_channel) {
> +        pid = nl_sock_pid(found_channel->sock);
> +    } else if (min_channel) {
> +        pid = nl_sock_pid(min_channel->sock);

This might be a question for Aaron mostly.

Could you, please, elaborate why we have a behavior change here?
Old code just returnd 0 as a pid, but after this change we will return
pid of a channel of port 0.

> +    }
> +
>      return pid;
>  }
>  
> @@ -2342,12 +2390,14 @@ dpif_netlink_operate(struct dpif *dpif_, struct dpif_op **ops, size_t n_ops,
>  static void
>  dpif_netlink_handler_uninit(struct dpif_handler *handler)
>  {
> +    hmap_destroy(&handler->channels);
>      vport_delete_sock_pool(handler);
>  }
>  
>  static int
>  dpif_netlink_handler_init(struct dpif_handler *handler)
>  {
> +    hmap_init(&handler->channels);
>      return vport_create_sock_pool(handler);
>  }
>  #else
> @@ -2355,6 +2405,7 @@ dpif_netlink_handler_init(struct dpif_handler *handler)
>  static int
>  dpif_netlink_handler_init(struct dpif_handler *handler)
>  {
> +    hmap_init(&handler->channels);
>      handler->epoll_fd = epoll_create(10);
>      return handler->epoll_fd < 0 ? errno : 0;
>  }
> @@ -2362,6 +2413,7 @@ dpif_netlink_handler_init(struct dpif_handler *handler)
>  static void
>  dpif_netlink_handler_uninit(struct dpif_handler *handler)
>  {
> +    hmap_destroy(&handler->channels);
>      close(handler->epoll_fd);
>  }
>  #endif
> @@ -2374,9 +2426,7 @@ static int
>  dpif_netlink_refresh_channels(struct dpif_netlink *dpif, uint32_t n_handlers)
>      OVS_REQ_WRLOCK(dpif->upcall_lock)
>  {
> -    unsigned long int *keep_channels;
>      struct dpif_netlink_vport vport;
> -    size_t keep_channels_nbits;
>      struct nl_dump dump;
>      uint64_t reply_stub[NL_DUMP_BUFSIZE / 8];
>      struct ofpbuf buf;
> @@ -2412,22 +2462,16 @@ dpif_netlink_refresh_channels(struct dpif_netlink *dpif, uint32_t n_handlers)
>  
>      for (i = 0; i < n_handlers; i++) {
>          struct dpif_handler *handler = &dpif->handlers[i];
> -

Please, keep.

>          handler->event_offset = handler->n_events = 0;
>      }
>  
> -    keep_channels_nbits = dpif->uc_array_size;
> -    keep_channels = bitmap_allocate(keep_channels_nbits);
> -
>      ofpbuf_use_stub(&buf, reply_stub, sizeof reply_stub);
>      dpif_netlink_port_dump_start__(dpif, &dump);
>      while (!dpif_netlink_port_dump_next__(dpif, &dump, &vport, &buf)) {
> -        uint32_t port_no = odp_to_u32(vport.port_no);
>          uint32_t upcall_pid;
>          int error;
>  
> -        if (port_no >= dpif->uc_array_size
> -            || !vport_get_pid(dpif, port_no, &upcall_pid)) {
> +        if (!vport_get_pid(dpif, vport.port_no, &upcall_pid)) {
>              struct nl_sock *sock;
>              error = create_nl_sock(dpif, &sock);
>  
> @@ -2475,25 +2519,15 @@ dpif_netlink_refresh_channels(struct dpif_netlink *dpif, uint32_t n_handlers)
>              }
>          }
>  
> -        if (port_no < keep_channels_nbits) {
> -            bitmap_set1(keep_channels, port_no);
> -        }
>          continue;
>  
>      error:
> -        vport_del_channels(dpif, vport.port_no);
> +        vport_del_channel(dpif, vport.port_no);
>      }
> +
>      nl_dump_done(&dump);
>      ofpbuf_uninit(&buf);
>  
> -    /* Discard any saved channels that we didn't reuse. */
> -    for (i = 0; i < keep_channels_nbits; i++) {
> -        if (!bitmap_is_set(keep_channels, i)) {
> -            vport_del_channels(dpif, u32_to_odp(i));
> -        }
> -    }
> -    free(keep_channels);
> -
>      return retval;
>  }
>  
> @@ -2714,6 +2748,8 @@ dpif_netlink_recv__(struct dpif_netlink *dpif, uint32_t handler_id,
>      OVS_REQ_RDLOCK(dpif->upcall_lock)
>  {
>      struct dpif_handler *handler;
> +    size_t n_channels;
> +
>      int read_tries = 0;
>  
>      if (!dpif->handlers || handler_id >= dpif->n_handlers) {
> @@ -2721,14 +2757,15 @@ dpif_netlink_recv__(struct dpif_netlink *dpif, uint32_t handler_id,
>      }
>  
>      handler = &dpif->handlers[handler_id];
> -    if (handler->event_offset >= handler->n_events) {
> +    n_channels = dpif_handler_channels_count(handler);
> +    if (handler->event_offset >= handler->n_events && n_channels) {
>          int retval;
>  
>          handler->event_offset = handler->n_events = 0;
>  
>          do {
>              retval = epoll_wait(handler->epoll_fd, handler->epoll_events,
> -                                dpif->uc_array_size, 0);
> +                                n_channels, 0);
>          } while (retval < 0 && errno == EINTR);
>  
>          if (retval < 0) {
> @@ -2741,7 +2778,10 @@ dpif_netlink_recv__(struct dpif_netlink *dpif, uint32_t handler_id,
>  
>      while (handler->event_offset < handler->n_events) {
>          int idx = handler->epoll_events[handler->event_offset].data.u32;
> -        struct dpif_channel *ch = &dpif->channels[idx];
> +        struct dpif_channel *ch = dpif_handler_channel_find(handler, idx);
> +        if (!ch) {
> +            return EAGAIN;

How can it be that handler received event on port that it doesn't have channel for?
Maybe assertion will be better here?

> +        }
>  
>          handler->event_offset++;
>  
> @@ -2845,12 +2885,14 @@ dpif_netlink_recv_purge__(struct dpif_netlink *dpif)
>      if (dpif->handlers) {
>          size_t i;
>  
> -        if (!dpif->channels[0].sock) {
> -            return;
> -        }
> -        for (i = 0; i < dpif->uc_array_size; i++ ) {
> +        for (i = 0; i < dpif->n_handlers; i++) {
> +            struct dpif_handler *handler = &dpif->handlers[i];
> +            struct dpif_channel *channel;
> +
> +            HMAP_FOR_EACH (channel, hmap_node, &handler->channels) {
> +                nl_sock_drain(channel->sock);
> +            }
>  
> -            nl_sock_drain(dpif->channels[i].sock);
>          }
>      }
>  }
> diff --git a/lib/id-pool.c b/lib/id-pool.c
> index 69910ad08..bef822f6b 100644
> --- a/lib/id-pool.c
> +++ b/lib/id-pool.c
> @@ -93,6 +93,16 @@ id_pool_find(struct id_pool *pool, uint32_t id)
>      return NULL;
>  }
>  
> +bool
> +id_pool_has_id(struct id_pool *pool, uint32_t id)
> +{
> +    if (!id_pool_find(pool, id)) {
> +        return false;
> +    }
> +
> +    return true;
> +}
> +
>  void
>  id_pool_add(struct id_pool *pool, uint32_t id)
>  {
> diff --git a/lib/id-pool.h b/lib/id-pool.h
> index 8721f8793..62876e2a5 100644
> --- a/lib/id-pool.h
> +++ b/lib/id-pool.h
> @@ -29,6 +29,7 @@ void id_pool_destroy(struct id_pool *);
>  bool id_pool_alloc_id(struct id_pool *, uint32_t *id);
>  void id_pool_free_id(struct id_pool *, uint32_t id);
>  void id_pool_add(struct id_pool *, uint32_t id);
> +bool id_pool_has_id(struct id_pool *, uint32_t id);
>  
>  /*
>   * ID pool.
> 



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