Make the two block layer operations most frequently used (REQ_OP_READ
and REQ_OP_WRITE) bypass the switch statements in the submission and
response paths. Assume these two enums are 0 and 1 which allows a
single comparison to select both of them. Check that assumption
at driver start-up.
Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
---
drivers/scsi/sd.c | 82 +++++++++++++++++++++++++++++++----------------
1 file changed, 55 insertions(+), 27 deletions(-)
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 4b1402633c36..9f047fd3c92d 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1227,6 +1227,14 @@ static int sd_init_command(struct scsi_cmnd *cmd)
{
struct request *rq = cmd->request;
+ /*
+ * Assumption that REQ_OP_READ and REQ_OP_WRITE are 0 and 1 is
+ * checked in init_sd(). The following "if" is done to dispatch
+ * REQ_OP_READ and REQ_OP_WRITE quickly.
+ */
+ if (likely(req_op(rq) < 2))
+ return sd_setup_read_write_cmnd(cmd);
+
switch (req_op(rq)) {
case REQ_OP_DISCARD:
switch (scsi_disk(rq->rq_disk)->provisioning_mode) {
@@ -1247,9 +1255,6 @@ static int sd_init_command(struct scsi_cmnd *cmd)
return sd_setup_write_same_cmnd(cmd);
case REQ_OP_FLUSH:
return sd_setup_flush_cmnd(cmd);
- case REQ_OP_READ:
- case REQ_OP_WRITE:
- return sd_setup_read_write_cmnd(cmd);
case REQ_OP_ZONE_REPORT:
return sd_zbc_setup_report_cmnd(cmd);
case REQ_OP_ZONE_RESET:
@@ -1973,30 +1978,12 @@ static int sd_done(struct scsi_cmnd *SCpnt)
int sense_valid = 0;
int sense_deferred = 0;
- switch (req_op(req)) {
- case REQ_OP_DISCARD:
- case REQ_OP_WRITE_ZEROES:
- case REQ_OP_WRITE_SAME:
- case REQ_OP_ZONE_RESET:
- if (!result) {
- good_bytes = blk_rq_bytes(req);
- scsi_set_resid(SCpnt, 0);
- } else {
- good_bytes = 0;
- scsi_set_resid(SCpnt, blk_rq_bytes(req));
- }
- break;
- case REQ_OP_ZONE_REPORT:
- if (!result) {
- good_bytes = scsi_bufflen(SCpnt)
- - scsi_get_resid(SCpnt);
- scsi_set_resid(SCpnt, 0);
- } else {
- good_bytes = 0;
- scsi_set_resid(SCpnt, blk_rq_bytes(req));
- }
- break;
- default:
+ /*
+ * Assumption that REQ_OP_READ and REQ_OP_WRITE are 0 and 1 is
+ * checked in init_sd(). The following "if" is done to expedite
+ * REQ_OP_READ and REQ_OP_WRITE.
+ */
+ if (likely(req_op(req) < 2)) {
/*
* In case of bogus fw or device, we could end up having
* an unaligned partial completion. Check this here and force
@@ -2011,6 +1998,36 @@ static int sd_done(struct scsi_cmnd *SCpnt)
round_up(resid, sector_size));
scsi_set_resid(SCpnt, resid);
}
+ } else {
+ switch (req_op(req)) {
+ case REQ_OP_DISCARD:
+ case REQ_OP_WRITE_ZEROES:
+ case REQ_OP_WRITE_SAME:
+ case REQ_OP_ZONE_RESET:
+ if (!result) {
+ good_bytes = blk_rq_bytes(req);
+ scsi_set_resid(SCpnt, 0);
+ } else {
+ good_bytes = 0;
+ scsi_set_resid(SCpnt, blk_rq_bytes(req));
+ }
+ break;
+ case REQ_OP_ZONE_REPORT:
+ if (!result) {
+ good_bytes = scsi_bufflen(SCpnt)
+ - scsi_get_resid(SCpnt);
+ scsi_set_resid(SCpnt, 0);
+ } else {
+ good_bytes = 0;
+ scsi_set_resid(SCpnt, blk_rq_bytes(req));
+ }
+ break;
+ default:
+ sd_printk(KERN_NOTICE, sdkp, "unexpected REQ_OP=%u\n",
+ (unsigned int)req_op(req));
+ WARN_ON_ONCE(true);
+ break;
+ }
}
if (result) {
@@ -3597,6 +3614,17 @@ static int __init init_sd(void)
int majors = 0, i, err;
SCSI_LOG_HLQUEUE(3, printk("init_sd: sd driver entry point\n"));
+ /*
+ * The sd_init_command() and sd_done() assume REQ_OP_READ and
+ * REQ_OP_WRITE are 0 and 1 and will fail if they are not. If they
+ * are not, would prefer a compile failure but the preprocessor can't
+ * use enum constants. Place check here because only need to check
+ * early and once.
+ */
+ if (REQ_OP_READ + REQ_OP_WRITE > 1)
+ pr_err("%s: REQ_OP_READ=%d REQ_OP_WRITE=%d %s.\n", __func__,
+ REQ_OP_READ, REQ_OP_WRITE,
+ "expected 0 and 1. Logic ERROR");
for (i = 0; i < SD_MAJORS; i++) {
if (register_blkdev(sd_major(i), "sd") != 0)
--
2.17.1
