From: Paolo Valente <paolo.valente@linaro.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
ulf.hansson@linaro.org, linus.walleij@linaro.org,
broonie@kernel.org, bfq-iosched@googlegroups.com,
oleksandr@natalenko.name, mancha@tower-research.com,
Paolo Valente <paolo.valente@linaro.org>
Subject: [PATCH BUGFIX IMPROVEMENT 02/14] block, bfq: avoid selecting a queue w/o budget
Date: Tue, 29 Jan 2019 12:06:26 +0100 [thread overview]
Message-ID: <20190129110638.12652-3-paolo.valente@linaro.org> (raw)
In-Reply-To: <20190129110638.12652-1-paolo.valente@linaro.org>
To boost throughput on devices with internal queueing and in scenarios
where device idling is not strictly needed, bfq immediately starts
serving a new bfq_queue if the in-service bfq_queue remains without
pending I/O, even if new I/O may arrive soon for the latter
queue. Then, if such I/O actually arrives soon, bfq preempts the new
in-service bfq_queue so as to give the previous queue a chance to go
on being served (in case the previous queue should actually be the one
to be served, according to its timestamps).
However, the in-service bfq_queue, say Q, may also be without further
budget when it remains also pending I/O. Since bfq changes budgets
dynamically to fit the needs of bfq_queues, this happens more often
than one may expect. If this happens, then there is no point in trying
to go on serving Q when new I/O arrives for it soon: Q would be
expired immediately after being selected for service. This would only
cause useless overhead. This commit avoids such a useless selection.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
block/bfq-iosched.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index c7a4a15c7c19..9ea2c4f42501 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1380,7 +1380,15 @@ static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
{
struct bfq_entity *entity = &bfqq->entity;
- if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) {
+ /*
+ * In the next compound condition, we check also whether there
+ * is some budget left, because otherwise there is no point in
+ * trying to go on serving bfqq with this same budget: bfqq
+ * would be expired immediately after being selected for
+ * service. This would only cause useless overhead.
+ */
+ if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
+ bfq_bfqq_budget_left(bfqq) > 0) {
/*
* We do not clear the flag non_blocking_wait_rq here, as
* the latter is used in bfq_activate_bfqq to signal
--
2.20.1
next prev parent reply other threads:[~2019-01-29 11:07 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-29 11:06 [PATCH BUGFIX IMPROVEMENT 00/14] batch of patches for next linux release Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 01/14] block, bfq: do not consider interactive queues in srt filtering Paolo Valente
2019-01-29 11:06 ` Paolo Valente [this message]
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 03/14] block, bfq: make sure queue budgets are not below service received Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 04/14] block, bfq: remove case of redirected bic from insert_request Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 05/14] block, bfq: consider also ioprio classes in symmetry detection Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 06/14] block, bfq: split function bfq_better_to_idle Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 07/14] block, bfq: do not plug I/O of in-service queue when harmful Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 08/14] block, bfq: unconditionally plug I/O in asymmetric scenarios Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 09/14] block, bfq: fix sequential rq detection in rate estimation Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 10/14] block, bfq: fix queue removal from weights tree Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 11/14] block, bfq: reduce threshold for detecting command queueing Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 12/14] block, bfq: port commit "cfq-iosched: improve hw_tag detection" Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 13/14] block, bfq: do not overcharge writes in asymmetric scenarios Paolo Valente
2019-01-29 11:06 ` [PATCH BUGFIX IMPROVEMENT 14/14] block, bfq: fix in-service-queue check for queue merging Paolo Valente
2019-01-31 19:50 ` [PATCH BUGFIX IMPROVEMENT 00/14] batch of patches for next linux release Jens Axboe
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