This is a note to let you know that I've just added the patch titled
s390/zcrypt: Fix wrong comparison leading to strange load balancing
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: s390-zcrypt-fix-wrong-comparison-leading-to-strange-load-balancing.patch and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Feb 1 13:45:42 CET 2018
From: Harald Freudenberger freude@linux.vnet.ibm.com Date: Fri, 17 Nov 2017 16:32:22 +0100 Subject: s390/zcrypt: Fix wrong comparison leading to strange load balancing
From: Harald Freudenberger freude@linux.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@linux.vnet.ibm.com Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/s390/crypto/zcrypt_api.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/s390/crypto/zcrypt_api.c +++ b/drivers/s390/crypto/zcrypt_api.c @@ -218,8 +218,8 @@ static inline bool zcrypt_queue_compare( 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; }
Patches currently in stable-queue which might be from freude@linux.vnet.ibm.com are
queue-4.14/s390-zcrypt-fix-wrong-comparison-leading-to-strange-load-balancing.patch