[SCSI] zfcp: optimize zfcp_qdio_account

Remove expensive ktime_get()/ktime_us_delta() functions from the hot
path and use get_clock_monotonic() instead. This elimates seven
function calls and avoids a lot of unnecessary calculations.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

2 files changed, 6 insertions, 7 deletions

diff --git a/drivers/s390/scsi/zfcp_def.h b/drivers/s390/scsi/zfcp_def.h
index cc98eead2c3c..7da2fad8f515 100644
--- a/drivers/s390/scsi/zfcp_def.h
+++ b/drivers/s390/scsi/zfcp_def.h
@@ -438,7 +438,7 @@ struct zfcp_qdio {
         struct zfcp_qdio_queue  req_q;
         spinlock_t              stat_lock;
         spinlock_t              req_q_lock;
-        ktime_t                 req_q_time;
+        unsigned long long      req_q_time;
         u64                     req_q_util;
         atomic_t                req_q_full;
         wait_queue_head_t       req_q_wq;
diff --git a/drivers/s390/scsi/zfcp_qdio.c b/drivers/s390/scsi/zfcp_qdio.c
index 2b499e28ff1f..6c5228b627fc 100644
--- a/drivers/s390/scsi/zfcp_qdio.c
+++ b/drivers/s390/scsi/zfcp_qdio.c
@@ -56,16 +56,15 @@ static void zfcp_qdio_zero_sbals(struct qdio_buffer *sbal[], int first, int cnt)
 }
 
 /* this needs to be called prior to updating the queue fill level */
-static void zfcp_qdio_account(struct zfcp_qdio *qdio)
+static inline void zfcp_qdio_account(struct zfcp_qdio *qdio)
 {
-        ktime_t now;
-        s64 span;
+        unsigned long long now, span;
         int free, used;
 
         spin_lock(&qdio->stat_lock);
-        now = ktime_get();
-        span = ktime_us_delta(now, qdio->req_q_time);
-        free = max(0, atomic_read(&qdio->req_q.count));
+        now = get_clock_monotonic();
+        span = (now - qdio->req_q_time) >> 12;
+        free = atomic_read(&qdio->req_q.count);
         used = QDIO_MAX_BUFFERS_PER_Q - free;
         qdio->req_q_util += used * span;
         qdio->req_q_time = now;