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authorTejun Heo <tj@kernel.org>2009-07-03 17:48:17 +0900
committerJens Axboe <jens.axboe@oracle.com>2009-09-11 14:33:30 +0200
commit80a761fd33cf812f771e212139157bf8f58d4b3f (patch)
tree21ea67ad749c15f25cb8a9278fe9bd7643c0ba31 /block/blk.h
parenta82afdfcb8c0df09776b6458af6b68fc58b2e87b (diff)
block: implement mixed merge of different failfast requests
Failfast has characteristics from other attributes. When issuing, executing and successuflly completing requests, failfast doesn't make any difference. It only affects how a request is handled on failure. Allowing requests with different failfast settings to be merged cause normal IOs to fail prematurely while not allowing has performance penalties as failfast is used for read aheads which are likely to be located near in-flight or to-be-issued normal IOs. This patch introduces the concept of 'mixed merge'. A request is a mixed merge if it is merge of segments which require different handling on failure. Currently the only mixable attributes are failfast ones (or lack thereof). When a bio with different failfast settings is added to an existing request or requests of different failfast settings are merged, the merged request is marked mixed. Each bio carries failfast settings and the request always tracks failfast state of the first bio. When the request fails, blk_rq_err_bytes() can be used to determine how many bytes can be safely failed without crossing into an area which requires further retrials. This allows request merging regardless of failfast settings while keeping the failure handling correct. This patch only implements mixed merge but doesn't enable it. The next one will update SCSI to make use of mixed merge. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Niel Lambrechts <niel.lambrechts@gmail.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block/blk.h')
-rw-r--r--block/blk.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/block/blk.h b/block/blk.h
index 3fae6add543..5ee3d7e72fe 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -104,6 +104,7 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req,
int attempt_back_merge(struct request_queue *q, struct request *rq);
int attempt_front_merge(struct request_queue *q, struct request *rq);
void blk_recalc_rq_segments(struct request *rq);
+void blk_rq_set_mixed_merge(struct request *rq);
void blk_queue_congestion_threshold(struct request_queue *q);