Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> On Tue, Aug 31, 2021 at 04:50:35PM +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@nvidia.com>
> > ---
> > 
> > changes from v1:
> >  - use param_set_uint_minmax (from Christoph)
> >  - added "Should > 0" to module description
> > 
> > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > ---
> >  drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> >  1 file changed, 19 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 4b49df2dfd23..9332fc4e9b31 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -24,6 +24,22 @@
> >  /* 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)
> > +{
> > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > +}
> > +
> > +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. Should > 0");
> > +
> >  static int major;
> >  static DEFINE_IDA(vd_index_ida);
> >  
> > @@ -501,7 +517,9 @@ 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);
> 
> If you respin, please consider calling them request queues. That's the
> terminology from the VIRTIO spec and it's nice to keep it consistent.
> But the purpose of num_io_queues is clear, so:
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

I did this:
+static unsigned int num_io_request_queues;
+module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
+MODULE_PARM_DESC(num_io_request_queues,
+                "Limit number of IO request virt queues to use for each device. 0 for now limit");