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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | SEE ALSO | AUTHORS | COLOPHON |
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IBV_GET_CQ_EVENT(3) Libibverbs Programmer's Manual IBV_GET_CQ_EVENT(3)
ibv_get_cq_event, ibv_ack_cq_events - get and acknowledge
completion queue (CQ) events
#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);
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.
ibv_get_cq_event() returns 0 on success, and -1 on error.
ibv_ack_cq_events() returns no value.
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().
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);
ibv_create_comp_channel(3), ibv_create_cq(3),
ibv_req_notify_cq(3), ibv_poll_cq(3)
Dotan Barak
<[email protected]>
This page is part of the rdma-core (RDMA Core Userspace Libraries
and Daemons) project. Information about the project can be found
at ⟨https://github.com/linux-rdma/rdma-core⟩. If you have a bug
report for this manual page, send it to
[email protected]. This page was obtained from the
project's upstream Git repository
⟨https://github.com/linux-rdma/rdma-core.git⟩ on 2023-12-22. (At
that time, the date of the most recent commit that was found in
the repository was 2023-12-20.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
libibverbs 2006-10-31 IBV_GET_CQ_EVENT(3)
Pages that refer to this page: ibv_create_comp_channel(3), ibv_create_cq(3), ibv_create_cq_ex(3)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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