Jens Axboe wrote:
On Wed, Apr 20 2005, Tejun Heo wrote:
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 <[email protected]>
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;
Do it on requeue, please - not on the initial spotting of the request.
The thing is that we also need to set REQ_SOFTBARRIER on
BLKPREP_DEFER. So, it will be two places - in elv_next_request and
blk_requeue_request. The end result will be the same. Do you think
doing on requeue paths is better?
--
tejun
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