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blk-mq: reduce unnecessary software queue looping 

In flush_busy_ctxs() and blk_mq_hctx_has_pending(), regardless of how many
ctxs assigned to one hctx, they will all loop hctx->ctx_map.map_size
times. Here hctx->ctx_map.map_size is a const ALIGN(nr_cpu_ids, 8) / 8.
Especially, flush_busy_ctxs() is in hot code path. And it's unnecessary.
Change ->map_size to contain the actually mapped software queues, so we
only loop for as many iterations as we have to.

And remove cpumask setting and nr_ctx count in blk_mq_init_cpu_queues()
since they are all re-done in blk_mq_map_swqueue().
blk_mq_map_swqueue().

Signed-off-by: Chong Yuan <chong.yuan@memblaze.com>
Reviewed-by: Wenbo Wang <wenbo.wang@memblaze.com>

Updated by me for formatting and commenting.

Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Chong Yuan 2015-04-15 11:39:29 -06:00 committed by Jens Axboe
parent dc48e56d76
commit 889fa31f00
1 changed files with 9 additions and 4 deletions
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13
block/blk-mq.c
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@ -1522,8 +1522,6 @@ static int blk_mq_alloc_bitmap(struct blk_mq_ctxmap *bitmap, int node)
if (!bitmap->map)
return -ENOMEM;
bitmap->map_size = num_maps;
total = nr_cpu_ids;
for (i = 0; i < num_maps; i++) {
bitmap->map[i].depth = min(total, bitmap->bits_per_word);
@ -1764,8 +1762,6 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
continue;
hctx = q->mq_ops->map_queue(q, i);
cpumask_set_cpu(i, hctx->cpumask);
hctx->nr_ctx++;
/*
* Set local node, IFF we have more than one hw queue. If
@ -1802,6 +1798,8 @@ static void blk_mq_map_swqueue(struct request_queue *q)
}
queue_for_each_hw_ctx(q, hctx, i) {
struct blk_mq_ctxmap *map = &hctx->ctx_map;
/*
* If no software queues are mapped to this hardware queue,
* disable it and free the request entries.
@ -1817,6 +1815,13 @@ static void blk_mq_map_swqueue(struct request_queue *q)
continue;
}
/*
* Set the map size to the number of mapped software queues.
* This is more accurate and more efficient than looping
* over all possibly mapped software queues.
*/
map->map_size = hctx->nr_ctx / map->bits_per_word;
/*
* Initialize batch roundrobin counts
*/