diff options
| author | Manoj N. Kumar <manoj@linux.vnet.ibm.com> | 2016-03-25 14:26:49 -0500 |
|---|---|---|
| committer | Martin K. Petersen <martin.petersen@oracle.com> | 2016-03-28 20:43:34 -0400 |
| commit | ea76543127da32dec28af0a13ea1b06625fc085e (patch) | |
| tree | 9112ed10ec3a8d4395f2964aa29510b7238dedc8 /drivers/scsi/cxlflash | |
| parent | 9526f36026f778e82b5175249443854c03b2e660 (diff) | |
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/cxlflash')
| -rw-r--r-- | drivers/scsi/cxlflash/main.c | 8 |
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; } |