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   ibv_ack_cq_events    ( 3 )

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Имя (Name)

ibv_get_cq_event, ibv_ack_cq_events - get and acknowledge
       completion queue (CQ) events

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Синопсис (Synopsis)

#include <infiniband/verbs.h>

       int ibv_get_cq_event(struct ibv_comp_channel *channel,
                            struct ibv_cq **cq, void **cq_context);

       void ibv_ack_cq_events(struct ibv_cq *cq, unsigned int nevents);

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Описание (Description)

ibv_get_cq_event() waits for the next completion event in the
       completion event channel channel.  Fills the arguments cq with
       the CQ that got the event and cq_context with the CQ's context.

       ibv_ack_cq_events() acknowledges nevents events on the CQ cq.

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Возвращаемое значение (Return value)

ibv_get_cq_event() returns 0 on success, and -1 on error.

       ibv_ack_cq_events() returns no value.

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Примечание (Note)

All completion events that ibv_get_cq_event() returns must be
       acknowledged using ibv_ack_cq_events().  To avoid races,
       destroying a CQ will wait for all completion events to be
       acknowledged; this guarantees a one-to-one correspondence between
       acks and successful gets.

       Calling ibv_ack_cq_events() may be relatively expensive in the
       datapath, since it must take a mutex.  Therefore it may be better
       to amortize this cost by keeping a count of the number of events
       needing acknowledgement and acking several completion events in
       one call to ibv_ack_cq_events().

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Примеры (Examples)

The following code example demonstrates one possible way to work
       with completion events. It performs the following steps:

       Stage I: Preparation
       1. Creates a CQ
       2. Requests for notification upon a new (first) completion event

       Stage II: Completion Handling Routine
       3. Wait for the completion event and ack it
       4. Request for notification upon the next completion event
       5. Empty the CQ

       Note that an extra event may be triggered without having a
       corresponding completion entry in the CQ.  This occurs if a
       completion entry is added to the CQ between Step 4 and Step 5,
       and the CQ is then emptied (polled) in Step 5.

       cq = ibv_create_cq(ctx, 1, ev_ctx, channel, 0);
       if (!cq) {
               fprintf(stderr, "Failed to create CQ\n");
               return 1;
       }

       /* Request notification before any completion can be created */
       if (ibv_req_notify_cq(cq, 0)) {
               fprintf(stderr, "Couldn't request CQ notification\n");
               return 1;
       }

       .
       .
       .

       /* Wait for the completion event */
       if (ibv_get_cq_event(channel, &ev_cq, &ev_ctx)) {
               fprintf(stderr, "Failed to get cq_event\n");
               return 1;
       }

       /* Ack the event */
       ibv_ack_cq_events(ev_cq, 1);

       /* Request notification upon the next completion event */
       if (ibv_req_notify_cq(ev_cq, 0)) {
               fprintf(stderr, "Couldn't request CQ notification\n");
               return 1;
       }

       /* Empty the CQ: poll all of the completions from the CQ (if any exist) */
       do {
               ne = ibv_poll_cq(cq, 1, &wc);
               if (ne < 0) {
                       fprintf(stderr, "Failed to poll completions from the CQ\n");
                       return 1;
               }

               /* there may be an extra event with no completion in the CQ */
               if (ne == 0)
                       continue;

               if (wc.status != IBV_WC_SUCCESS) {
                       fprintf(stderr, "Completion with status 0x%x was found\n", wc.status);
                       return 1;
               }
       } while (ne);

       The following code example demonstrates one possible way to work
       with completion events in non-blocking mode.  It performs the
       following steps:

       1. Set the completion event channel to be non-blocked
       2. Poll the channel until there it has a completion event
       3. Get the completion event and ack it

       /* change the blocking mode of the completion channel */
       flags = fcntl(channel->fd, F_GETFL);
       rc = fcntl(channel->fd, F_SETFL, flags | O_NONBLOCK);
       if (rc < 0) {
            fprintf(stderr, "Failed to change file descriptor of completion event channel\n");
            return 1;
       }

       /*
        * poll the channel until it has an event and sleep ms_timeout
        * milliseconds between any iteration
        */
       my_pollfd.fd      = channel->fd;
       my_pollfd.events  = POLLIN;
       my_pollfd.revents = 0;

       do {
            rc = poll(&my_pollfd, 1, ms_timeout);
       } while (rc == 0);
       if (rc < 0) {
            fprintf(stderr, "poll failed\n");
            return 1;
       }
       ev_cq = cq;

       /* Wait for the completion event */
       if (ibv_get_cq_event(channel, &ev_cq, &ev_ctx)) {
               fprintf(stderr, "Failed to get cq_event\n");
               return 1;
       }

       /* Ack the event */
       ibv_ack_cq_events(ev_cq, 1);

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Смотри также (See also)

ibv_create_comp_channel(3), ibv_create_cq(3),
       ibv_req_notify_cq(3), ibv_poll_cq(3)

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