[RFC PATCH 4/5] streamline some logical operations

[Douglas Gilbert <dgilbert@xxxxxxxxxxxx>]

Re-arrange some logic to lessen the number of checks. With logical
ANDs put the least likely first, with logical ORs put the most
likely first. Also add conditional hints on the assumed fastpath.

Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
---
 drivers/scsi/sd.c | 43 ++++++++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 9f047fd3c92d..05014054e357 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1171,9 +1171,9 @@ static int sd_setup_read_write_cmnd(struct scsi_cmnd *cmd)
 
 	fua = (rq->cmd_flags & REQ_FUA) ? 0x8 : 0;
 	dix = scsi_prot_sg_count(cmd);
-	dif = scsi_host_dif_capable(cmd->device->host, sdkp->protection_type);
+	dif = scsi_host_dif_capable(sdp->host, sdkp->protection_type);
 
-	if (write && dix)
+	if (dix && write)
 		sd_dif_prepare(cmd);
 
 	if (dif || dix)
@@ -1181,19 +1181,27 @@ static int sd_setup_read_write_cmnd(struct scsi_cmnd *cmd)
 	else
 		protect = 0;
 
-	if (protect && sdkp->protection_type == T10_PI_TYPE2_PROTECTION) {
+	if (unlikely(protect &&
+		     sdkp->protection_type == T10_PI_TYPE2_PROTECTION))
 		ret = sd_setup_read_write_32_cmnd(cmd, write, lba, nr_blocks,
 						  protect | fua);
-	} else if (sdp->use_16_for_rw || (nr_blocks > 0xffff)) {
+	else if (sdp->use_16_for_rw)
 		ret = sd_setup_read_write_16_cmnd(cmd, write, lba, nr_blocks,
 						  protect | fua);
-	} else if ((nr_blocks > 0xff) || (lba > 0x1fffff) || sdp->use_10_for_rw
-		   || protect) {
-		ret = sd_setup_read_write_10_cmnd(cmd, write, lba, nr_blocks,
-						  protect | fua);
-	} else {
-		ret = sd_setup_read_write_6_cmnd(cmd, write, lba, nr_blocks,
-						 protect | fua);
+	else if (likely(nr_blocks < 0x100)) {
+		if (sdp->use_10_for_rw || (lba > 0x1fffff) || protect)
+			ret = sd_setup_read_write_10_cmnd(cmd, write, lba,
+						 nr_blocks, protect | fua);
+		else
+			ret = sd_setup_read_write_6_cmnd(cmd, write, lba,
+						 nr_blocks, protect | fua);
+	} else {	/* not already done and nr_blocks > 0xff */
+		if (unlikely(nr_blocks > 0xffff))
+			ret = sd_setup_read_write_16_cmnd(cmd, write, lba,
+						 nr_blocks, protect | fua);
+		else
+			ret = sd_setup_read_write_10_cmnd(cmd, write, lba,
+						 nr_blocks, protect | fua);
 	}
 
 	if (ret != BLKPREP_OK)
@@ -1976,7 +1984,6 @@ static int sd_done(struct scsi_cmnd *SCpnt)
 	struct scsi_disk *sdkp = scsi_disk(SCpnt->request->rq_disk);
 	struct request *req = SCpnt->request;
 	int sense_valid = 0;
-	int sense_deferred = 0;
 
 	/*
 	 * Assumption that REQ_OP_READ and REQ_OP_WRITE are 0 and 1 is
@@ -2030,16 +2037,14 @@ static int sd_done(struct scsi_cmnd *SCpnt)
 		}
 	}
 
-	if (result) {
+	if (unlikely(result)) {
 		sense_valid = scsi_command_normalize_sense(SCpnt, &sshdr);
-		if (sense_valid)
-			sense_deferred = scsi_sense_is_deferred(&sshdr);
+		if (driver_byte(result) == DRIVER_SENSE ||
+		    (sense_valid && (!scsi_sense_is_deferred(&sshdr))))
+			good_bytes = sd_done_sense(SCpnt, good_bytes, &sshdr);
 	}
-	sdkp->medium_access_timed_out = 0;
 
-	if (unlikely(driver_byte(result) == DRIVER_SENSE ||
-		     (sense_valid && !sense_deferred)))
-		good_bytes = sd_done_sense(SCpnt, good_bytes, &sshdr);
+	sdkp->medium_access_timed_out = 0;
 
 	if (sd_is_zoned(sdkp))
 		sd_zbc_complete(SCpnt, good_bytes, &sshdr);
-- 
2.17.1