[openib-general] Question On mad.c

[Sean Hefty]

Devesh Sharma wrote:
> In mad.c while calling ib_post_receive() operation
> 
>       spin_lock_irqsave(&recv_queue->lock, flags);
> 
>        post = (++recv_queue->count < recv_queue->max_active);
> 
>        list_add_tail(&mad_priv->header.mad_list.list, &recv_queue->list);
>        spin_unlock_irqrestore(&recv_queue->lock, flags);
>        ret = ib_post_recv(qp_info->qp, &recv_wr, &bad_recv_wr);
> 
> This is in while loop till "post" variable remains true, value of
> max_active is 512 So loop will go 512 times.
> 
> If the qp on which this posting is going on dose not supports 512
> recevie  descriptors posting then what will happen?
> Although during qp creation max_recv supported will be returned but
> loop is independent of this.

The QP is created with a size of IB_MAD_QP_RECV_SIZE (512).  If the hardware 
cannot support this size of a QP, then the create QP call will fail.  I.e. the 
hardware can provide a QP that is larger, but not smaller.  The code cannot 
adjust to using a larger size without resizing the corresponding CQ, which is 
not yet supported.

- Sean