linux-kernel - [patch v11 4/6] block, bfq: do not idle if only one group is activated

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Message-Id: <20220916071942.214222-5-yukuai1@huaweicloud.com>
Date:   Fri, 16 Sep 2022 15:19:40 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     tj@...nel.org, axboe@...nel.dk, paolo.valente@...aro.org,
        jack@...e.cz
Cc:     cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yukuai3@...wei.com,
        yukuai1@...weicloud.com, yi.zhang@...wei.com
Subject: [patch v11 4/6] block, bfq: do not idle if only one group is activated

From: Yu Kuai <yukuai3@...wei.com>

Now that root group is counted into 'num_groups_with_pending_reqs',
'num_groups_with_pending_reqs > 0' is always true in
bfq_asymmetric_scenario(). Thus change the condition to '> 1'.

On the other hand, this change can enable concurrent sync io if only
one group is activated.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 block/bfq-iosched.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 970b302a7a3e..6d95b0e488a8 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -820,7 +820,7 @@ bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
  * much easier to maintain the needed state:
  * 1) all active queues have the same weight,
  * 2) all active queues belong to the same I/O-priority class,
- * 3) there are no active groups.
+ * 3) there is at most one active group.
  * In particular, the last condition is always true if hierarchical
  * support or the cgroups interface are not enabled, thus no state
  * needs to be maintained in this case.
@@ -852,7 +852,7 @@ static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
 
 	return varied_queue_weights || multiple_classes_busy
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
-	       || bfqd->num_groups_with_pending_reqs > 0
+	       || bfqd->num_groups_with_pending_reqs > 1
 #endif
 		;
 }
-- 
2.31.1