This is a note to let you know that I've just added the patch titled
scsi: virtio_scsi: limit number of hw queues by nr_cpu_ids
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
scsi-virtio_scsi-limit-number-of-hw-queues-by-nr_cpu_ids.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1978f30a87732d4d9072a20abeded9fe17884f1b Mon Sep 17 00:00:00 2001
From: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Date: Wed, 27 Mar 2019 18:36:35 +0800
Subject: scsi: virtio_scsi: limit number of hw queues by nr_cpu_ids
From: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
commit 1978f30a87732d4d9072a20abeded9fe17884f1b upstream.
When tag_set->nr_maps is 1, the block layer limits the number of hw queues
by nr_cpu_ids. No matter how many hw queues are used by virtio-scsi, as it
has (tag_set->nr_maps == 1), it can use at most nr_cpu_ids hw queues.
In addition, specifically for pci scenario, when the 'num_queues' specified
by qemu is more than maxcpus, virtio-scsi would not be able to allocate
more than maxcpus vectors in order to have a vector for each queue. As a
result, it falls back into MSI-X with one vector for config and one shared
for queues.
Considering above reasons, this patch limits the number of hw queues used
by virtio-scsi by nr_cpu_ids.
Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Kunkun Jiang <jiangkunkun@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/scsi/virtio_scsi.c | 1 +
1 file changed, 1 insertion(+)
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -853,6 +853,7 @@ static int virtscsi_probe(struct virtio_
/* We need to know how many queues before we allocate. */
num_queues = virtscsi_config_get(vdev, num_queues) ? : 1;
+ num_queues = min_t(unsigned int, nr_cpu_ids, num_queues);
num_targets = virtscsi_config_get(vdev, max_target) + 1;
Patches currently in stable-queue which might be from dongli.zhang@xxxxxxxxxx are
queue-4.19/scsi-virtio_scsi-limit-number-of-hw-queues-by-nr_cpu_ids.patch
