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Commit 7074f076 authored by Paolo Valente's avatar Paolo Valente Committed by Jens Axboe
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block, bfq: do not tag totally seeky queues as soft rt 



Sync random I/O is likely to be confused with soft real-time I/O,
because it is characterized by limited throughput and apparently
isochronous arrival pattern. To avoid false positives, this commits
prevents bfq_queues containing only random (seeky) I/O from being
tagged as soft real-time.

Tested-by: default avatarHolger Hoffstätte <holger@applied-asynchrony.com>
Tested-by: default avatarOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 8cacc5ab

block/bfq-iosched.c

+14 −0
Original line number Diff line number Diff line
@@ -242,6 +242,14 @@ static struct kmem_cache *bfq_pool; 
	  blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT))

#define BFQQ_CLOSE_THR		(sector_t)(8 * 1024)

#define BFQQ_SEEKY(bfqq)	(hweight32(bfqq->seek_history) > 19)

/*

 * Sync random I/O is likely to be confused with soft real-time I/O,

 * because it is characterized by limited throughput and apparently

 * isochronous arrival pattern. To avoid false positives, queues

 * containing only random (seeky) I/O are prevented from being tagged

 * as soft real-time.

 */

#define BFQQ_TOTALLY_SEEKY(bfqq)	(bfqq->seek_history & -1)



/* Min number of samples required to perform peak-rate update */

#define BFQ_RATE_MIN_SAMPLES	32
@@ -1622,6 +1630,7 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd, 
	 */

	in_burst = bfq_bfqq_in_large_burst(bfqq);

	soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&

		!BFQQ_TOTALLY_SEEKY(bfqq) &&

		!in_burst &&

		time_is_before_jiffies(bfqq->soft_rt_next_start) &&

		bfqq->dispatched == 0;
@@ -4816,6 +4825,11 @@ bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq, 
{

	bfqq->seek_history <<= 1;

	bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq);



	if (bfqq->wr_coeff > 1 &&

	    bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&

	    BFQQ_TOTALLY_SEEKY(bfqq))

		bfq_bfqq_end_wr(bfqq);

}



static void bfq_update_has_short_ttime(struct bfq_data *bfqd,