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ibv_query_srq()

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int ibv_query_srq(struct ibv_srq *srq, struct ibv_srq_attr *srq_attr);

Description

ibv_query_srq() returns the attributes of a Shared Receive Queue.

struct ibv_srq_attr describes the attributes of the Shared Receive Queue.

struct ibv_srq_attr {
        uint32_t                max_wr;
        uint32_t                max_sge;
        uint32_t                srq_limit;
};

Here is the full description of struct ibv_srq_attr:

max_wr The maximum number of outstanding Work Requests that can be posted to this Shared Receive Queue
max_sge The maximum number of scatter/gather elements in any Work Request that can be posted to this Shared Receive Queue
srq_limit The value that the SRQ is armed with. 0 means that the SRQ limit event won’t be generated (since the number of outstanding WRs in the SRQ can’t be negative)

Parameters

Name Direction Description
srq in SRQ that was returned from ibv_create_srq()
srq_attr out The current SRQ attributed will be filled in it

Return Values

Value Description
0 On success
errno On failure
ENOMEM Not enough resources to complete this operation
ENOSYS Query Shared Receive Queue isn’t supported by this RDMA device

Examples

Query an SRQ for its attributes:

struct ibv_srq *srq;
struct ibv_srq_attr srq_attr;
 
if (ibv_query_srq(srq, &srq_attr)) {
	fprintf(stderr, "Error, ibv_query_srq() failed\n");
	return -1;
}

FAQs

Calling every time to ibv_query_srq() when I need an SRQ attribute takes time, can I cache some of the attributes?

Actually, yes. The attributes, which indicates the SRQ size, i.e. max_wr and max_sge, won't change unless this SRQ will be resized using ibv_modify_srq(). The srq_limit value may change: when the SRQ is armed, it will hold the low watermark value. After the SRQ limit event will be generated, it will hold the value 0 (unless the SRQ will be rearmed again).

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