linux-kernel - [PATCH AUTOSEL 5.15 20/29] block: reduce kblockd_mod_delayed_work

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Message-Id: <20211221015751.116328-20-sashal@kernel.org>
Date:   Mon, 20 Dec 2021 20:57:41 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>, Dexuan Cui <decui@...rosoft.com>,
        Ming Lei <ming.lei@...hat.com>,
        Sasha Levin <sashal@...nel.org>, linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 20/29] block: reduce kblockd_mod_delayed_work_on() CPU consumption

From: Jens Axboe <axboe@...nel.dk>

[ Upstream commit cb2ac2912a9ca7d3d26291c511939a41361d2d83 ]

Dexuan reports that he's seeing spikes of very heavy CPU utilization when
running 24 disks and using the 'none' scheduler. This happens off the
sched restart path, because SCSI requires the queue to be restarted async,
and hence we're hammering on mod_delayed_work_on() to ensure that the work
item gets run appropriately.

Avoid hammering on the timer and just use queue_work_on() if no delay
has been specified.

Reported-and-tested-by: Dexuan Cui <decui@...rosoft.com>
Link: https://lore.kernel.org/linux-block/BYAPR21MB1270C598ED214C0490F47400BF719@BYAPR21MB1270.namprd21.prod.outlook.com/
Reviewed-by: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index c2d912d0c976c..a728434fcff87 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1625,6 +1625,8 @@ EXPORT_SYMBOL(kblockd_schedule_work);
 int kblockd_mod_delayed_work_on(int cpu, struct delayed_work *dwork,
 				unsigned long delay)
 {
+	if (!delay)
+		return queue_work_on(cpu, kblockd_workqueue, &dwork->work);
 	return mod_delayed_work_on(cpu, kblockd_workqueue, dwork, delay);
 }
 EXPORT_SYMBOL(kblockd_mod_delayed_work_on);
-- 
2.34.1