IB/qib: Precompute timeout jiffies to optimize latency

A new field is added to qib_qp called timeout_jiffies. It is
initialized upon create and modify.

The field is now used instead of a computation based on qp->timeout.

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

3 files changed, 11 insertions, 6 deletions

diff --git a/drivers/infiniband/hw/qib/qib_qp.c b/drivers/infiniband/hw/qib/qib_qp.c
index 500981bce9c0..7e7e16fbee99 100644
--- a/drivers/infiniband/hw/qib/qib_qp.c
+++ b/drivers/infiniband/hw/qib/qib_qp.c
@@ -801,8 +801,12 @@ int qib_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr,
         if (attr_mask & IB_QP_MIN_RNR_TIMER)
                 qp->r_min_rnr_timer = attr->min_rnr_timer;
 
-        if (attr_mask & IB_QP_TIMEOUT)
+        if (attr_mask & IB_QP_TIMEOUT) {
                 qp->timeout = attr->timeout;
+                qp->timeout_jiffies =
+                        usecs_to_jiffies((4096UL * (1UL << qp->timeout)) /
+                                1000UL);
+        }
 
         if (attr_mask & IB_QP_QKEY)
                 qp->qkey = attr->qkey;
@@ -1034,6 +1038,9 @@ struct ib_qp *qib_create_qp(struct ib_pd *ibpd,
                         goto bail_swq;
                 }
                 RCU_INIT_POINTER(qp->next, NULL);
+                qp->timeout_jiffies =
+                        usecs_to_jiffies((4096UL * (1UL << qp->timeout)) /
+                                1000UL);
                 if (init_attr->srq)
                         sz = 0;
                 else {
diff --git a/drivers/infiniband/hw/qib/qib_rc.c b/drivers/infiniband/hw/qib/qib_rc.c
index 5d77cb8aa052..ecfa087ad45e 100644
--- a/drivers/infiniband/hw/qib/qib_rc.c
+++ b/drivers/infiniband/hw/qib/qib_rc.c
@@ -59,8 +59,7 @@ static void start_timer(struct qib_qp *qp)
         qp->s_flags |= QIB_S_TIMER;
         qp->s_timer.function = rc_timeout;
         /* 4.096 usec. * (1 << qp->timeout) */
-        qp->s_timer.expires = jiffies +
-                usecs_to_jiffies((4096UL * (1UL << qp->timeout)) / 1000UL);
+        qp->s_timer.expires = jiffies + qp->timeout_jiffies;
         add_timer(&qp->s_timer);
 }
 
@@ -1519,9 +1518,7 @@ read_middle:
                  * 4.096 usec. * (1 << qp->timeout)
                  */
                 qp->s_flags |= QIB_S_TIMER;
-                mod_timer(&qp->s_timer, jiffies +
-                        usecs_to_jiffies((4096UL * (1UL << qp->timeout)) /
-                                         1000UL));
+                mod_timer(&qp->s_timer, jiffies + qp->timeout_jiffies);
                 if (qp->s_flags & QIB_S_WAIT_ACK) {
                         qp->s_flags &= ~QIB_S_WAIT_ACK;
                         qib_schedule_send(qp);
diff --git a/drivers/infiniband/hw/qib/qib_verbs.h b/drivers/infiniband/hw/qib/qib_verbs.h
index d7b6109528a4..0c19ef0c4123 100644
--- a/drivers/infiniband/hw/qib/qib_verbs.h
+++ b/drivers/infiniband/hw/qib/qib_verbs.h
@@ -496,6 +496,7 @@ struct qib_qp {
         u32 s_last;             /* last completed entry */
         u32 s_ssn;              /* SSN of tail entry */
         u32 s_lsn;              /* limit sequence number (credit) */
+        unsigned long timeout_jiffies;  /* computed from timeout */
         struct qib_swqe *s_wq;  /* send work queue */
         struct qib_swqe *s_wqe;
         struct qib_rq r_rq;             /* receive work queue */