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block, bfq: boost the throughput with random I/O on NCQ-capable HDDs 

This patch is basically the counterpart, for NCQ-capable rotational
devices, of the previous patch. Exactly as the previous patch does on
flash-based devices and for any workload, this patch disables device
idling on rotational devices, but only for random I/O. In fact, only
with these queues disabling idling boosts the throughput on
NCQ-capable rotational devices. To not break service guarantees,
idling is disabled for NCQ-enabled rotational devices only when the
same symmetry conditions considered in the previous patches hold.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Paolo Valente 2017-04-12 18:23:19 +02:00 committed by Jens Axboe
parent bf2b79e7c4
commit e01eff01d5
1 changed files with 6 additions and 10 deletions
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16
block/bfq-iosched.c
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@ -6439,20 +6439,15 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
* The next variable takes into account the cases where idling
* boosts the throughput.
*
* The value of the variable is computed considering that
* idling is usually beneficial for the throughput if:
* The value of the variable is computed considering, first, that
* idling is virtually always beneficial for the throughput if:
* (a) the device is not NCQ-capable, or
* (b) regardless of the presence of NCQ, the device is rotational
* and the request pattern for bfqq is I/O-bound (possible
* throughput losses caused by granting idling to seeky queues
* are mitigated by the fact that, in all scenarios where
* boosting throughput is the best thing to do, i.e., in all
* symmetric scenarios, only a minimal idle time is allowed to
* seeky queues).
* and the request pattern for bfqq is I/O-bound and sequential.
*
* Secondly, and in contrast to the above item (b), idling an
* NCQ-capable flash-based device would not boost the
* throughput even with intense I/O; rather it would lower
* throughput even with sequential I/O; rather it would lower
* the throughput in proportion to how fast the device
* is. Accordingly, the next variable is true if any of the
* above conditions (a) and (b) is true, and, in particular,
@ -6460,7 +6455,8 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
* device.
*/
idling_boosts_thr = !bfqd->hw_tag ||
(!blk_queue_nonrot(bfqd->queue) && bfq_bfqq_IO_bound(bfqq));
(!blk_queue_nonrot(bfqd->queue) && bfq_bfqq_IO_bound(bfqq) &&
bfq_bfqq_idle_window(bfqq));
/*
* The value of the next variable,