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authorManoj N. Kumar <manoj@linux.vnet.ibm.com>2016-03-25 22:26:49 +0300
committerMartin K. Petersen <martin.petersen@oracle.com>2016-03-29 03:43:34 +0300
commitea76543127da32dec28af0a13ea1b06625fc085e (patch)
tree9112ed10ec3a8d4395f2964aa29510b7238dedc8 /drivers/scsi
parent9526f36026f778e82b5175249443854c03b2e660 (diff)
downloadlinux-ea76543127da32dec28af0a13ea1b06625fc085e.tar.xz
cxlflash: Move to exponential back-off when cmd_room is not available
While profiling the cxlflash_queuecommand() path under a heavy load it was found that number of retries to find cmd_room was fairly high. There are two problems with the current back-off: a) It starts with a udelay of 0 b) It backs-off linearly Tried several approaches (a higher multiple 10*n, 100*n, as well as n^2, 2^n) and found that the exponential back-off(2^n) approach had the least overall cost. Cost as being defined as overall time spent waiting. The fix is to change the linear back-off to an exponential back-off. This solution also takes care of the problem with the initial delay (starts with 1 usec). Signed-off-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com> Acked-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Uma Krishnan <ukrishn@linux.vnet.ibm.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Diffstat (limited to 'drivers/scsi')
-rw-r--r--drivers/scsi/cxlflash/main.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/drivers/scsi/cxlflash/main.c b/drivers/scsi/cxlflash/main.c
index 1d418073d621..724b77189ee7 100644
--- a/drivers/scsi/cxlflash/main.c
+++ b/drivers/scsi/cxlflash/main.c
@@ -289,7 +289,7 @@ static void context_reset(struct afu_cmd *cmd)
atomic64_set(&afu->room, room);
if (room)
goto write_rrin;
- udelay(nretry);
+ udelay(1 << nretry);
} while (nretry++ < MC_ROOM_RETRY_CNT);
pr_err("%s: no cmd_room to send reset\n", __func__);
@@ -303,7 +303,7 @@ write_rrin:
if (rrin != 0x1)
break;
/* Double delay each time */
- udelay(2 << nretry);
+ udelay(1 << nretry);
} while (nretry++ < MC_ROOM_RETRY_CNT);
}
@@ -338,7 +338,7 @@ retry:
atomic64_set(&afu->room, room);
if (room)
goto write_ioarrin;
- udelay(nretry);
+ udelay(1 << nretry);
} while (nretry++ < MC_ROOM_RETRY_CNT);
dev_err(dev, "%s: no cmd_room to send 0x%X\n",
@@ -352,7 +352,7 @@ retry:
* afu->room.
*/
if (nretry++ < MC_ROOM_RETRY_CNT) {
- udelay(nretry);
+ udelay(1 << nretry);
goto retry;
}