On Mon, Aug 30, 2021 at 03:00:23PM +0300, Max Gurtovoy wrote:
> Sometimes a user would like to control the amount of IO queues to be
> created for a block device. For example, for limiting the memory
> footprint of virtio-blk devices.
>
> Signed-off-by: Max Gurtovoy <mgurtovoy@xxxxxxxxxx>
Hmm. It's already limited by # of CPUs... Why not just limit
from the hypervisor side? What's the actual use-case here?
> ---
> drivers/block/virtio_blk.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index e574fbf5e6df..77e8468e8593 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -24,6 +24,28 @@
> /* The maximum number of sg elements that fit into a virtqueue */
> #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>
> +static int virtblk_queue_count_set(const char *val,
> + const struct kernel_param *kp)
> +{
> + unsigned int n;
> + int ret;
> +
> + ret = kstrtouint(val, 10, &n);
> + if (ret != 0 || n > nr_cpu_ids)
> + return -EINVAL;
> + return param_set_uint(val, kp);
> +}
> +
> +static const struct kernel_param_ops queue_count_ops = {
> + .set = virtblk_queue_count_set,
> + .get = param_get_uint,
> +};
> +
> +static unsigned int num_io_queues;
> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> +MODULE_PARM_DESC(num_io_queues,
> + "Number of IO virt queues to use for blk device.");
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
> @@ -501,7 +523,9 @@ static int init_vq(struct virtio_blk *vblk)
> if (err)
> num_vqs = 1;
>
> - num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> + num_vqs = min_t(unsigned int,
> + min_not_zero(num_io_queues, nr_cpu_ids),
> + num_vqs);
>
> vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> if (!vblk->vqs)
> --
> 2.18.1
