IB/rdmavt, staging/rdma/hfi1: use qps to dynamically scale timeout value

A busy_jiffies variable is maintained and updated when rc qps are
created and deleted. busy_jiffies is a scaled value of the number
of rc qps in the device. busy_jiffies is incremented every rc qp
scaling interval. busy_jiffies is added to the rc timeout
in add_retry_timer and mod_retry_timer. The rc qp scaling interval
is selected based on extensive performance evaluation of targeted
workloads.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Vennila Megavannan <vennila.megavannan@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

include/rdma/rdma_vt.h

@@ -318,7 +318,9 @@ struct rvt_dev_info {
 	/* QP */
 	struct rvt_qp_ibdev *qp_dev;
 	u32 n_qps_allocated;    /* number of QPs allocated for device */
-	spinlock_t n_qps_lock; /* keep track of number of qps */
+	u32 n_rc_qps;		/* number of RC QPs allocated for device */
+	u32 busy_jiffies;	/* timeout scaling based on RC QP count */
+	spinlock_t n_qps_lock;	/* protect qps, rc qps and busy jiffy counts */
 
 	/* memory maps */
 	struct list_head pending_mmaps;