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ibv_poll_cq

NAME

ibv_poll_cq - poll a completion queue (CQ)

SYNOPSIS

 #include <infiniband/verbs.h>
 
 int ibv_poll_cq(struct ibv_cq *cq, int num_entries,
                 struct ibv_wc *wc);
 

DESCRIPTION

ibv_poll_cq() polls the CQ cq for work completions and returns the first num_entries (or all available completions if the CQ contains fewer than this number) in the array wc. The argument wc is a pointer to an array of ibv_wc structs, as defined in <infiniband/verbs.h>.

 struct ibv_wc {
 uint64_t                wr_id;          /* ID of the completed Work Request (WR) */
 enum ibv_wc_status      status;         /* Status of the operation */
 enum ibv_wc_opcode      opcode;         /* Operation type specified in the completed WR */
 uint32_t                vendor_err;     /* Vendor error syndrome */
 uint32_t                byte_len;       /* Number of bytes transferred */
 uint32_t                imm_data;       /* Immediate data (in network byte order) */
 uint32_t                qp_num;         /* Local QP number of completed WR */
 uint32_t                src_qp;         /* Source QP number (remote QP number) of completed WR (valid only for UD QPs) */
 int                     wc_flags;       /* Flags of the completed WR */
 uint16_t                pkey_index;     /* P_Key index (valid only for GSI QPs) */
 uint16_t                slid;           /* Source LID */
 uint8_t                 sl;             /* Service Level */
 uint8_t                 dlid_path_bits; /* DLID path bits (not applicable for multicast messages) */
 };
 
 

The attribute wc_flags describes the properties of the work completion. It is either 0 or the bitwise OR of one or more of the following flags:

IBV_WC_GRH GRH is present (valid only for UD QPs)

IBV_WC_WITH_IMM Immediate data value is valid

Not all wc attributes are always valid. If the completion status is other than IBV_WC_SUCCESS, only the following attributes are valid: wr_id, status, qp_num, and vendor_err.

RETURN VALUE

On success, ibv_poll_cq() returns a non-negative value equal to the number of completions found. On failure, a negative value is returned.

NOTES

Each polled completion is removed from the CQ and cannot be returned to it.

The user should consume work completions at a rate that prevents CQ overrun from occurrence. In case of a CQ overrun, the async event IBV_EVENT_CQ_ERR will be triggered, and the CQ cannot be used.

SEE ALSO

ibv_post_send(3), ibv_post_recv(3)

AUTHORS

Dotan Barak <dotanba@gmail.com>