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    Subject[PATCH AUTOSEL 5.0 65/79] virtio-blk: limit number of hw queues by nr_cpu_ids
    Date
    From: Dongli Zhang <dongli.zhang@oracle.com>

    [ 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>
    ---
    drivers/block/virtio_blk.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
    index b16a887bbd02..29bede887237 100644
    --- a/drivers/block/virtio_blk.c
    +++ b/drivers/block/virtio_blk.c
    @@ -513,6 +513,8 @@ static int init_vq(struct virtio_blk *vblk)
    if (err)
    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);
    if (!vblk->vqs)
    return -ENOMEM;
    --
    2.19.1
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