linux-kernel - [PATCH AUTOSEL for 4.14 024/100] s390/zcrypt: Fix wrong comparison leading to strange load balancing

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Date:   Wed, 24 Jan 2018 04:14:34 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Harald Freudenberger <freude@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.14 024/100] s390/zcrypt: Fix wrong comparison
 leading to strange load balancing

From: Harald Freudenberger <freude@...ux.vnet.ibm.com>

[ Upstream commit 0b0882672640ced4deeebf84da0b88b6389619c4 ]

The function to decide if one zcrypt queue is better than
another one compared two pointers instead of comparing the
values where the pointers refer to. So within the same
zcrypt card when load of each queue was equal just one queue
was used. This effect only appears on relatively lite load,
typically with one thread applications.

This patch fixes the wrong comparison and now the counters
show that requests are balanced equally over all available
queues within the cards.

There is no performance improvement coming with this fix.
As long as the queue depth for an APQN queue is not touched,
processing is not faster when requests are spread over
queues within the same card hardware. So this fix only
beautifies the lszcrypt counter printouts.

Signed-off-by: Harald Freudenberger <freude@...ux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/s390/crypto/zcrypt_api.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/crypto/zcrypt_api.c b/drivers/s390/crypto/zcrypt_api.c
index b5f4006198b9..a9a56aa9c26b 100644
--- a/drivers/s390/crypto/zcrypt_api.c
+++ b/drivers/s390/crypto/zcrypt_api.c
@@ -218,8 +218,8 @@ static inline bool zcrypt_queue_compare(struct zcrypt_queue *zq,
 	weight += atomic_read(&zq->load);
 	pref_weight += atomic_read(&pref_zq->load);
 	if (weight == pref_weight)
-		return &zq->queue->total_request_count >
-			&pref_zq->queue->total_request_count;
+		return zq->queue->total_request_count >
+			pref_zq->queue->total_request_count;
 	return weight > pref_weight;
 }

-- 
2.11.0