From 9934c8c04561413609d2bc38c6b9f268cba774a4 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 8 May 2009 11:54:16 +0900 Subject: block: implement and enforce request peek/start/fetch Till now block layer allowed two separate modes of request execution. A request is always acquired from the request queue via elv_next_request(). After that, drivers are free to either dequeue it or process it without dequeueing. Dequeue allows elv_next_request() to return the next request so that multiple requests can be in flight. Executing requests without dequeueing has its merits mostly in allowing drivers for simpler devices which can't do sg to deal with segments only without considering request boundary. However, the benefit this brings is dubious and declining while the cost of the API ambiguity is increasing. Segment based drivers are usually for very old or limited devices and as converting to dequeueing model isn't difficult, it doesn't justify the API overhead it puts on block layer and its more modern users. Previous patches converted all block low level drivers to dequeueing model. This patch completes the API transition by... * renaming elv_next_request() to blk_peek_request() * renaming blkdev_dequeue_request() to blk_start_request() * adding blk_fetch_request() which is combination of peek and start * disallowing completion of queued (not started) requests * applying new API to all LLDs Renamings are for consistency and to break out of tree code so that it's apparent that out of tree drivers need updating. [ Impact: block request issue API cleanup, no functional change ] Signed-off-by: Tejun Heo Cc: Rusty Russell Cc: James Bottomley Cc: Mike Miller Cc: unsik Kim Cc: Paul Clements Cc: Tim Waugh Cc: Geert Uytterhoeven Cc: David S. Miller Cc: Laurent Vivier Cc: Jeff Garzik Cc: Jeremy Fitzhardinge Cc: Grant Likely Cc: Adrian McMenamin Cc: Stephen Rothwell Cc: Bartlomiej Zolnierkiewicz Cc: Borislav Petkov Cc: Sergei Shtylyov Cc: Alex Dubov Cc: Pierre Ossman Cc: David Woodhouse Cc: Markus Lidel Cc: Stefan Weinhuber Cc: Martin Schwidefsky Cc: Pete Zaitcev Cc: FUJITA Tomonori Signed-off-by: Jens Axboe --- block/blk-tag.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'block/blk-tag.c') diff --git a/block/blk-tag.c b/block/blk-tag.c index 3c518e3303a..c260f7c30dd 100644 --- a/block/blk-tag.c +++ b/block/blk-tag.c @@ -374,7 +374,7 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq) rq->cmd_flags |= REQ_QUEUED; rq->tag = tag; bqt->tag_index[tag] = rq; - blkdev_dequeue_request(rq); + blk_start_request(rq); list_add(&rq->queuelist, &q->tag_busy_list); return 0; } -- cgit v1.2.3-18-g5258 From 0a7ae2ff0d29bb3b327edff4c8ab67b3834fa811 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Wed, 20 May 2009 08:54:31 +0200 Subject: block: change the tag sync vs async restriction logic Make them fully share the tag space, but disallow async requests using the last any two slots. Signed-off-by: Jens Axboe --- block/blk-tag.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) (limited to 'block/blk-tag.c') diff --git a/block/blk-tag.c b/block/blk-tag.c index c260f7c30dd..2e5cfeb5933 100644 --- a/block/blk-tag.c +++ b/block/blk-tag.c @@ -336,7 +336,7 @@ EXPORT_SYMBOL(blk_queue_end_tag); int blk_queue_start_tag(struct request_queue *q, struct request *rq) { struct blk_queue_tag *bqt = q->queue_tags; - unsigned max_depth, offset; + unsigned max_depth; int tag; if (unlikely((rq->cmd_flags & REQ_QUEUED))) { @@ -355,13 +355,16 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq) * to starve sync IO on behalf of flooding async IO. */ max_depth = bqt->max_depth; - if (rq_is_sync(rq)) - offset = 0; - else - offset = max_depth >> 2; + if (!rq_is_sync(rq) && max_depth > 1) { + max_depth -= 2; + if (!max_depth) + max_depth = 1; + if (q->in_flight[0] > max_depth) + return 1; + } do { - tag = find_next_zero_bit(bqt->tag_map, max_depth, offset); + tag = find_first_zero_bit(bqt->tag_map, max_depth); if (tag >= max_depth) return 1; -- cgit v1.2.3-18-g5258