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

Aaron Conole aconole at redhat.com
Thu Sep 17 19:49:49 UTC 2020


Ilya Maximets <i.maximets at ovn.org> writes:

> 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.

Agreed.

>> +        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.

I see what you mean - previously, we only got pid for index 0 when the
port index was out of range.  Now we will get it even when the port
index is in range, but not found.  That shouldn't be - it is my mistake.

>> +    }
>> +
>>      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?

Hrrm... I guess the only case I can imagine is if during upcall
processing we remove a port?  I don't know if it can actually happen
though.  I agree, maybe an assert / log would be better.

>> +        }
>>  
>>          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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