int ibv_modify_srq(struct ibv_srq *srq,
                   struct ibv_srq_attr *srq_attr,
                   enum ibv_srq_attr_mask srq_attr_mask);

Description

ibv_modify_srq() modifies 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:

srq_attr_mask specifies the SRQ attributes to be modified. It is either 0 or the bitwise OR of one or more of the following flags:

The suggested way to use the SRQ limit event mechanism is:
1) Create the SRQ
2) Post WRs to that SRQ (before or after QPs have been associated with it)
3) Arm the SRQ limit to a non-zero value that is less than the number of posted WRs
4) When the number of outstanding WRs in the SRQ will drop below the limit, the asynchronous event IBV_EVENT_SRQ_LIMIT_REACHED will be generated. When this happens, one should perform the following:

a) Acknowledge the asynchronous event
b) Goto 2) (i.e. post more WRs to the SRQ and set the SRQ limit)

If an SRQ limit is being set to a value, which is greater than the current number of outstanding WRs in the SRQ, an SRQ limit event will be generated immediately.

Parameters

Return Values

Examples

1) Resize an SRQ:

struct ibv_srq *srq;
struct ibv_srq_attr srq_attr;
 
memset(&srq_attr, 0, sizeof(srq_attr));
 
srq_attr.max_wr  = 10;
srq_attr.max_sge = 1;
 
if (ibv_modify_srq(srq, &srq_attr, IBV_SRQ_MAX_WR)) {
	fprintf(stderr, "Error, ibv_modify_srq() failed when resizing an SRQ\n");
	return -1;
}

2) Set a limit event to an SRQ:

struct ibv_srq *srq;
struct ibv_srq_attr srq_attr;
 
memset(&srq_attr, 0, sizeof(srq_attr));
 
srq_attr.srq_limit = 10;
 
if (ibv_modify_srq(srq, &srq_attr, IBV_SRQ_LIMIT)) {
	fprintf(stderr, "Error, ibv_modify_srq() failed when arming an SRQ\n");
	return -1;
}

FAQs

ibv_modify_srq() failed, what are the attributes of that SRQ now?

Exactly the same as before calling ibv_modify_srq(), no change was made to the SRQ.

I armed the SRQ with the value X. Can I change this value to Y?

Yes, you can. Just call ibv_modify_srq() with a different SRQ limit value.

Written by: Dotan Barak on December 8, 2012.on February 18, 2015.