Commit 0e8e67b8 authored Mar 27, 2019 by Dongli Zhang Committed by Greg Kroah-Hartman May 10, 2019

virtio-blk: limit number of hw queues by nr_cpu_ids



[ Upstream commit bf348f9b78d413e75bb079462751a1d86b6de36c ]

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-blk, 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-blk 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-blk by nr_cpu_ids.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent d955bb0b

drivers/block/virtio_blk.c

+2 −0

Original line number	Original line	Diff line number	Diff line
	@@ -446,6 +446,8 @@ static int init_vq(struct virtio_blk *vblk)
	if (err)		if (err)
	num_vqs = 1;		num_vqs = 1;

			num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);

	vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);		vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
	if (!vblk->vqs)		if (!vblk->vqs)
	return -ENOMEM;		return -ENOMEM;