scsi_debug: skip long delays when ndelay small

Commit Message

Douglas Gilbert July 12, 2018, 5:35 p.m. UTC

A test program's runtime became impractically long since any non
zero ndelay (e.g. 1 nanosec) caused Start Stop Unit to delay
over 8 magnitudes greater than other commands. This patch skips
long delays (on Start Stop Unit and Synchronize Cache) if ndelay
is less than or equal to 10 microsecs.

Signed-off-by: Douglas Gilbert <[e-mail]>
---
This patch is against MKP's 4.19/scsi-queue branch.

Re-arrange if condition so least likely is first part of && .

 drivers/scsi/scsi_debug.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Comments

Martin K. Petersen July 13, 2018, 3:03 a.m. UTC | #1

Doug,

> A test program's runtime became impractically long since any non zero
> ndelay (e.g. 1 nanosec) caused Start Stop Unit to delay over 8
> magnitudes greater than other commands. This patch skips long delays
> (on Start Stop Unit and Synchronize Cache) if ndelay is less than or
> equal to 10 microsecs.

Applied to 4.19/scsi-queue, thanks!

Patch

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 24d7496cd9e2..4dda192b8fba 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5790,11 +5790,13 @@  static int scsi_debug_queuecommand(struct Scsi_Host *shost,
 fini:
 	if (F_DELAY_OVERR & flags)
 		return schedule_resp(scp, devip, errsts, pfp, 0, 0);
-	else if ((sdebug_jdelay || sdebug_ndelay) && (flags & F_LONG_DELAY)) {
+	else if ((flags & F_LONG_DELAY) && (sdebug_jdelay > 0 ||
+					    sdebug_ndelay > 10000)) {
 		/*
-		 * If any delay is active, for F_SSU_DELAY want at least 1
-		 * second and if sdebug_jdelay>0 want a long delay of that
-		 * many seconds; for F_SYNC_DELAY want 1/20 of that.
+		 * Skip long delays if ndelay <= 10 microseconds. Otherwise
+		 * for Start Stop Unit (SSU) want at least 1 second delay and
+		 * if sdebug_jdelay>1 want a long delay of that many seconds.
+		 * For Synchronize Cache want 1/20 of SSU's delay.
 		 */
 		int jdelay = (sdebug_jdelay < 2) ? 1 : sdebug_jdelay;
 		int denom = (flags & F_SYNC_DELAY) ? 20 : 1;