linux-kernel - [PATCH 4.9 44/78] s390/cio: add cond_resched() in the slow_eval_known

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Message-Id: <20200901150926.958300203@linuxfoundation.org>
Date:   Tue,  1 Sep 2020 17:10:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 44/78] 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 39a2b0cde9e42..d81fdcd6a1fe0 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