linux-master/block/bfq-iosched.c

156 BFQ_BFQQ_FNS(sync);
164 /* Expiration time of async (0) and sync (1) requests, in ns. */
183  * When a sync request is dispatched, the queue that contains that
189  * w.r.t. to sync I/O, and it is done to counter the tendency of async
676  * Async I/O can easily starve sync I/O (both sync reads and sync
677  * writes), by consuming all tags. Similarly, storms of sync writes,
678  * such as those that sync(2) may trigger, can starve sync reads.
679  * Limit depths of async I/O and sync writes so as to counter both
721 	bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
826  * queue must receive.  If bfqq does sync I/O, then these are the only
1841 	 * - it is sync,
2385 	const int sync = rq_is_sync(rq);
2394 	bfqq->queued[sync]--;
2928 		 * Make sure also that bfqq is sync, because
2931 		 * sync queue, but this bfqq is async
3235 	 * Disallow merge of a sync bio into an async request.
3722  * example is sync random I/O on flash storage with command
3838  * arrival of new I/O requests for bfqq (recall that bfqq is sync). If
3983 	bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
4104 	 * the finish time of bfqq must be kept in sync with the
4246  *     of a request is waited for when a sync queue becomes idle,
4555 	 * sync non-weight-raised queue, to get a lower number of
4922 		 * a process that does some sync. A sync generates
5874 			      * Extra group reference, w.r.t. sync
6490  * allowed to switch to another queue---because bfqq is sync and
7093 	 * leaving 25% of tags only for sync reads.
7104 	 * no more than 75% of tags for sync writes (25% extra tags
7105 	 * w.r.t. async I/O, to prevent async I/O from starving sync
7112 	 * raised: leaving ~63% of tags for sync reads. This is the
7119 	/* no more than ~37% of tags for sync writes (~20% extra tags) */
7512  * parameters, but this timeout is used for both sync and async.