linux-kernel - [PATCH -next 06/11] block, bfq: do not idle if only one cgroup is activated

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Message-ID: <20220305091205.4188398-7-yukuai3@huawei.com>
Date:   Sat, 5 Mar 2022 17:12:00 +0800
From:   Yu Kuai <yukuai3@...wei.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>,
        <yi.zhang@...wei.com>
Subject: [PATCH -next 06/11] block, bfq: do not idle if only one cgroup is activated

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 'num_groups_with_pending_reqs > 1', so
it's consistent without counting root group.

On the other hand, with the following patches to only count groups(not
ancestors) with pending requests, sync io can be handled concurrently
if only one group has pending requests.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 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 3bc7a7686aad..07027dc9dc4c 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -812,7 +812,7 @@ 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 are one active groups at most.
  * 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.
@@ -844,7 +844,7 @@ 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