Re: [PATCH scsi-misc-2.6 01/05] scsi: make blk layer set REQ_SOFTBARRIER when a request is dispatched

Tejun Heo
2005-04-19T23:16:25Z

01_scsi_blk_make_started_requests_ordered.patch

Reordering already started requests is without any real
benefit and causes problems if the request has its
driver-specific resources allocated (as in SCSI). This patch
makes elv_next_request() set REQ_SOFTBARRIER automatically
when a request is dispatched.

As both as and cfq schedulers don't allow passing requeued
requests, the only behavior change is that requests deferred
by prep_fn won't be passed by other requests. This change
shouldn't cause any problem. The only affected driver other
than SCSI is i2o_block.

Signed-off-by: Tejun Heo <htejun@gmail.com>

elevator.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)

Index: scsi-reqfn-export/drivers/block/elevator.c
===================================================================
--- scsi-reqfn-export.orig/drivers/block/elevator.c 2005-04-20 08:13:01.000000000 +0900
+++ scsi-reqfn-export/drivers/block/elevator.c 2005-04-20 08:13:33.000000000 +0900
@@ -370,11 +370,11 @@ struct request *elv_next_request(request

while ((rq = __elv_next_request(q)) != NULL) {
/*
- * just mark as started even if we don't start it, a request
- * that has been delayed should not be passed by new incoming
- * requests
+ * just mark as started even if we don't start it.
+ * also, as a request that has been delayed should not
+ * be passed by new incoming requests, set softbarrier.
*/
- rq->flags |= REQ_STARTED;
+ rq->flags |= REQ_STARTED | REQ_SOFTBARRIER;

if (rq == q->last_merge)
q->last_merge = NULL;