scsi: mpi3mr: A performance fix

Commit 0c52310 ("hrtimer: Ignore slack time for RT tasks in
schedule_hrtimeout_range()") effectivelly shortens a sleep in a polling
function in the driver.  That is causing a performance regression as the
new value of just 2us is too low, in certain tests the perf drop is ~30%.
Fix this by adjusting the sleep to 20us (close to the previous value).

Reported-by: Jan Jurca <[email protected]>
Signed-off-by: Tomas Henzl <[email protected]>
Acked-by: Sumit Saxena <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Martin K. Petersen <[email protected]>

Author: thenzl

drivers/scsi/mpi3mr/mpi3mr.h

@@ -178,7 +178,7 @@ extern atomic64_t event_counter;
 #define MPI3MR_DEFAULT_SDEV_QD	32
 
 /* Definitions for Threaded IRQ poll*/
-#define MPI3MR_IRQ_POLL_SLEEP			2
+#define MPI3MR_IRQ_POLL_SLEEP			20
 #define MPI3MR_IRQ_POLL_TRIGGER_IOCOUNT		8
 
 /* Definitions for the controller security status*/

drivers/scsi/mpi3mr/mpi3mr_fw.c

@@ -728,7 +728,7 @@ static irqreturn_t mpi3mr_isr_poll(int irq, void *privdata)
 			    mpi3mr_process_op_reply_q(mrioc,
 				intr_info->op_reply_q);
 
-		usleep_range(MPI3MR_IRQ_POLL_SLEEP, 10 * MPI3MR_IRQ_POLL_SLEEP);
+		usleep_range(MPI3MR_IRQ_POLL_SLEEP, MPI3MR_IRQ_POLL_SLEEP + 1);
 
 	} while (atomic_read(&intr_info->op_reply_q->pend_ios) &&
 	    (num_op_reply < mrioc->max_host_ios));