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 <[email protected]> Signed-off-by: Arianna Avanzini <[email protected]> --- block/cfq-iosched.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 7fee23b..ae17421 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -38,7 +38,9 @@ * Even better for latency, BFQ explicitly privileges the I/O of two * classes of time-sensitive applications: interactive and soft * real-time. This feature enables BFQ to provide applications in - * these classes with a very low latency. + * these classes with a very low latency. Finally, BFQ also features + * additional heuristics for preserving both a low latency and a high + * throughput on NCQ-capable, rotational or flash-based devices. * * With respect to the version of BFQ presented in [1], and in the * papers cited therein, this implementation adds a hierarchical @@ -5629,20 +5631,15 @@ 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, @@ -5650,7 +5647,8 @@ 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, @@ -7457,7 +7455,7 @@ static int __init bfq_init(void) if (ret) goto err_pol_unreg; - pr_info("BFQ I/O-scheduler: v6"); + pr_info("BFQ I/O-scheduler: v7r3"); return 0; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
