diff options
Diffstat (limited to 'block/blk-tag.c')
| -rw-r--r-- | block/blk-tag.c | 22 |
1 files changed, 16 insertions, 6 deletions
diff --git a/block/blk-tag.c b/block/blk-tag.c index ed5166fbc59..c0d419e84ce 100644 --- a/block/blk-tag.c +++ b/block/blk-tag.c @@ -29,7 +29,7 @@ EXPORT_SYMBOL(blk_queue_find_tag); * __blk_free_tags - release a given set of tag maintenance info * @bqt: the tag map to free * - * Tries to free the specified @bqt@. Returns true if it was + * Tries to free the specified @bqt. Returns true if it was * actually freed and false if there are still references using it */ static int __blk_free_tags(struct blk_queue_tag *bqt) @@ -78,7 +78,7 @@ void __blk_queue_free_tags(struct request_queue *q) * blk_free_tags - release a given set of tag maintenance info * @bqt: the tag map to free * - * For externally managed @bqt@ frees the map. Callers of this + * For externally managed @bqt frees the map. Callers of this * function must guarantee to have released all the queues that * might have been using this tag map. */ @@ -94,7 +94,7 @@ EXPORT_SYMBOL(blk_free_tags); * @q: the request queue for the device * * Notes: - * This is used to disabled tagged queuing to a device, yet leave + * This is used to disable tagged queuing to a device, yet leave * queue in function. **/ void blk_queue_free_tags(struct request_queue *q) @@ -271,7 +271,7 @@ EXPORT_SYMBOL(blk_queue_resize_tags); * @rq: the request that has completed * * Description: - * Typically called when end_that_request_first() returns 0, meaning + * Typically called when end_that_request_first() returns %0, meaning * all transfers have been done for a request. It's important to call * this function before end_that_request_last(), as that will put the * request back on the free list thus corrupting the internal tag list. @@ -337,6 +337,7 @@ 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; int tag; if (unlikely((rq->cmd_flags & REQ_QUEUED))) { @@ -350,10 +351,19 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq) /* * Protect against shared tag maps, as we may not have exclusive * access to the tag map. + * + * We reserve a few tags just for sync IO, since we don't want + * 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; + do { - tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth); - if (tag >= bqt->max_depth) + tag = find_next_zero_bit(bqt->tag_map, max_depth, offset); + if (tag >= max_depth) return 1; } while (test_and_set_bit_lock(tag, bqt->tag_map)); |