[ovs-dev] [PATCH v7] dpif-netlink: distribute polling to discreet handlers

Mark Gray mark.d.gray at redhat.com
Wed Sep 9 14:12:58 UTC 2020


On 09/09/2020 14:49, Flavio Leitner wrote:
> 
> 
> Hi Mark,
> 
> Found one issue, and then since another spin is needed I am
> suggesting a stylish improvement.
> 
> 
> On Tue, Sep 08, 2020 at 06:27:48PM +0100, 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 | 325 +++++++++++++++++++++++++--------------------
>>  lib/id-pool.c      |  10 ++
>>  lib/id-pool.h      |   1 +
>>  3 files changed, 195 insertions(+), 141 deletions(-)
>>
>> diff --git a/lib/dpif-netlink.c b/lib/dpif-netlink.c
>> index 7da4fb54d..4ecf0c51c 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;
>> +    struct dpif_handler *handler;
>> +    uint32_t port_idx;
>>      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. */
>> +
>>  #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 */
>>  
>>      /* 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)
>> +{
>> +    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;
>> @@ -452,161 +496,145 @@ static bool
>>  vport_get_pid(struct dpif_netlink *dpif, uint32_t port_idx,
>>                uint32_t *upcall_pid)
>>  {
>> -    /* 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) {
>> +    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);
>> +        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);
>> +    struct dpif_channel *channel = NULL;
>> +    bool found_channel = false;
>>      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;
>> +        channel = dpif_handler_channel_find(&dpif->handlers[i],
>> +                                            odp_to_u32(port_no));
>> +        if (channel) {
>> +            dpif_channel_del(dpif, channel);
>> +            found_channel = true;
>> +            break;
>> +        }
> 
> My suggestion is to move channel declaration there to inside the loop
> without initialization and take out the found_channel like it is
> done at vport_get_pid():
> 
>     for (i = 0; i < dpif->n_handlers; i++) {
>         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;
>         }
>     }
> 
>     return false;

Makes sense, I dont like returning successfully mid-function but
probably makes it a bit easier to read.

> 
> 
>>      }
>> -#ifndef _WIN32
>> -    nl_sock_destroy(dpif->channels[port_idx].sock);
>> -#endif
>> -    dpif->channels[port_idx].sock = NULL;
>> +
>> +    return found_channel;
>>  }
>>  
>>  static void
>>  destroy_all_channels(struct dpif_netlink *dpif)
>>      OVS_REQ_WRLOCK(dpif->upcall_lock)
>>  {
> [...]
>> @@ -2475,25 +2520,15 @@ 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, port_no);
> 
> The port_no here is uint32_t but vport_del_channel() receives odp_port_t.
> That breaks build:
> https://travis-ci.org/github/fleitner/ovs/jobs/725370855

I see you set this up on your own github account. Good idea.

> 
> Thanks!
> 



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