Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1622309

[PATCH V4 08/16] block, bfq: preserve a low latency also with NCQ-capable drives

Show all headers | View raw

I/O schedulers typically allow NCQ-capable drives to prefetch I/O
requests, as NCQ boosts the throughput exactly by prefetching and
internally reordering requests.

Unfortunately, as discussed in detail and shown experimentally in [1],
this may cause fairness and latency guarantees to be violated. The
main problem is that the internal scheduler of an NCQ-capable drive
may postpone the service of some unlucky (prefetched) requests as long
as it deems serving other requests more appropriate to boost the
throughput.

This patch addresses this issue by not disabling device idling for
weight-raised queues, even if the device supports NCQ. This allows BFQ
to start serving a new queue, and therefore allows the drive to
prefetch new requests, only after the idling timeout expires. At that
time, all the outstanding requests of the expired queue have been most
certainly served.

[1] P. Valente and M. Andreolini, "Improving Application
    Responsiveness with the BFQ Disk I/O Scheduler", Proceedings of
    the 5th Annual International Systems and Storage Conference
    (SYSTOR '12), June 2012.
    Slightly extended version:
    http://algogroup.unimore.it/people/paolo/disk_sched/bfq-v1-suite-
							results.pdf

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
---
 block/bfq-iosched.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 7f94ad3..574a5f6 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6233,7 +6233,8 @@ static void bfq_update_idle_window(struct bfq_data *bfqd,
 
 	if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
 	    bfqd->bfq_slice_idle == 0 ||
-		(bfqd->hw_tag && BFQQ_SEEKY(bfqq)))
+		(bfqd->hw_tag && BFQQ_SEEKY(bfqq) &&
+			bfqq->wr_coeff == 1))
 		enable_idle = 0;
 	else if (bfq_sample_valid(bfqq->ttime.ttime_samples)) {
 		if (bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle &&
-- 
2.10.0

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH V4 00/16] Introduce the BFQ I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:30 +0200
  [PATCH V4 03/16] block, bfq: improve throughput boosting Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:30 +0200
  [PATCH V4 15/16] block, bfq: remove all get and put of I/O contexts Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:30 +0200
  [PATCH V4 13/16] block, bfq: boost the throughput with random I/O on NCQ-capable HDDs Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:30 +0200
  [PATCH V4 08/16] block, bfq: preserve a low latency also with NCQ-capable drives Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:30 +0200
  [PATCH V4 14/16] block, bfq: handle bursts of queue activations Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:40 +0200
  [PATCH V4 05/16] block, bfq: add more fairness with writes and slow processes Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:40 +0200
  [PATCH V4 09/16] block, bfq: reduce latency during request-pool saturation Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:40 +0200
  [PATCH V4 07/16] block, bfq: reduce I/O latency for soft real-time applications Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:40 +0200
  [PATCH V4 04/16] block, bfq: modify the peak-rate estimator Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:40 +0200
  [PATCH V4 11/16] block, bfq: reduce idling only in symmetric scenarios Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:40 +0200
  [PATCH V4 12/16] block, bfq: boost the throughput on NCQ-capable flash-based devices Paolo Valente <paolo.valente@linaro.org> - 2017-04-12 18:40 +0200
  Re: [PATCH V4 00/16] Introduce the BFQ I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2017-04-19 11:30 +0200
    Re: [PATCH V4 00/16] Introduce the BFQ I/O scheduler Jens Axboe <axboe@kernel.dk> - 2017-04-19 16:40 +0200
      Re: [PATCH V4 00/16] Introduce the BFQ I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2017-04-19 21:10 +0200
        Re: [PATCH V4 00/16] Introduce the BFQ I/O scheduler Jens Axboe <axboe@kernel.dk> - 2017-04-19 21:40 +0200

csiph-web