linux-kernel - [PATCH BUGFIX/IMPROVEMENT 2/4] block, bfq: always update the budget of an entity when needed

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Message-Id: <20180816165118.17402-3-paolo.valente@linaro.org>
Date:   Thu, 16 Aug 2018 18:51:16 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, linus.walleij@...aro.org,
        broonie@...nel.org, bfq-iosched@...glegroups.com,
        oleksandr@...alenko.name, Paolo Valente <paolo.valente@...aro.org>
Subject: [PATCH BUGFIX/IMPROVEMENT 2/4] block, bfq: always update the budget of an entity when needed

When the next child entity to serve changes for a given parent entity,
the budget of that parent entity must be updated accordingly.
Unfortunately, this update is not performed, by mistake, for the
entities that happen to switch from having no child entity to serve,
to having one child entity to serve.

Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 block/bfq-wf2q.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index dbc07b456059..d558fd26740c 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -130,10 +130,14 @@ static bool bfq_update_next_in_service(struct bfq_sched_data *sd,
 	if (!change_without_lookup) /* lookup needed */
 		next_in_service = bfq_lookup_next_entity(sd, expiration);
 
-	if (next_in_service)
-		parent_sched_may_change = !sd->next_in_service ||
+	if (next_in_service) {
+		bool new_budget_triggers_change =
 			bfq_update_parent_budget(next_in_service);
 
+		parent_sched_may_change = !sd->next_in_service ||
+			new_budget_triggers_change;
+	}
+
 	sd->next_in_service = next_in_service;
 
 	if (!next_in_service)
-- 
2.16.1