linux-kernel - [PATCH AUTOSEL 4.4 3/6] s390/cio: add cond_resched() in the slow_eval_known

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Date:   Mon, 24 Aug 2020 12:39:40 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Sasha Levin <sashal@...nel.org>, linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 4.4 3/6] s390/cio: add cond_resched() in the slow_eval_known_fn() loop

From: Vineeth Vijayan <vneethv@...ux.ibm.com>

[ Upstream commit 0b8eb2ee9da1e8c9b8082f404f3948aa82a057b2 ]

The scanning through subchannels during the time of an event could
take significant amount of time in case of platforms with lots of
known subchannels. This might result in higher scheduling latencies
for other tasks especially on systems with a single CPU. Add
cond_resched() call, as the loop in slow_eval_known_fn() can be
executed for a longer duration.

Reviewed-by: Peter Oberparleiter <oberpar@...ux.ibm.com>
Signed-off-by: Vineeth Vijayan <vneethv@...ux.ibm.com>
Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/s390/cio/css.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 8ecc956ecb59c..370a3a2c6de73 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -529,6 +529,11 @@ static int slow_eval_known_fn(struct subchannel *sch, void *data)
 		rc = css_evaluate_known_subchannel(sch, 1);
 		if (rc == -EAGAIN)
 			css_schedule_eval(sch->schid);
+		/*
+		 * The loop might take long time for platforms with lots of
+		 * known devices. Allow scheduling here.
+		 */
+		cond_resched();
 	}
 	return 0;
 }
-- 
2.25.1