Re: [PATCH v3 1/1] virtio-blk: add num_request_queues module parameter

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

On Sun, Oct 24, 2021 at 11:12:26AM +0300, Max Gurtovoy wrote:
> 
> On 10/24/2021 10:19 AM, Max Gurtovoy wrote:
> > 
> > On 10/22/2021 12:30 PM, Michael S. Tsirkin wrote:
> > > On Thu, Sep 02, 2021 at 11:46:22PM +0300, Max Gurtovoy wrote:
> > > > Sometimes a user would like to control the amount of request queues to
> > > > be created for a block device. For example, for limiting the memory
> > > > footprint of virtio-blk devices.
> > > > 
> > > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > ---
> > > > 
> > > > changes from v2:
> > > >   - renamed num_io_queues to num_request_queues (from Stefan)
> > > >   - added Reviewed-by signatures (from Stefan and Christoph)
> > > > 
> > > > 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 | 21 ++++++++++++++++++++-
> > > >   1 file changed, 20 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > index 4b49df2dfd23..aaa2833a4734 100644
> > > > --- a/drivers/block/virtio_blk.c
> > > > +++ b/drivers/block/virtio_blk.c
> > > > @@ -24,6 +24,23 @@
> > > >   /* 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);
> > > > +}
> > > > +
> 
> BTW, I've noticed in your new message you allow setting 0 so you might want
> to change the code to
> 
> param_set_uint_minmax(val, kp, 0, nr_cpu_ids);
> 
> to a case a user will load the module with num_request_queues=0.

Oh. So as written the default forces 1 queue?
Send a patch please!

> > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > +    .set = virtblk_queue_count_set,
> > > > +    .get = param_get_uint,
> > > > +};
> > > > +
> > > > +static unsigned int num_request_queues;
> > > > +module_param_cb(num_request_queues, &queue_count_ops,
> > > > &num_request_queues,
> > > > +        0644);
> > > > +MODULE_PARM_DESC(num_request_queues,
> > > > +         "Number of request queues to use for blk device.
> > > > Should > 0");
> > > > +
> > > >   static int major;
> > > >   static DEFINE_IDA(vd_index_ida);
> > > I wasn't happy with the message here so I tweaked it.
> > > 
> > > Please look at it in linux-next and confirm. Thanks!
> > 
> > Looks good.
> > 
> > 
> > > 
> > > 
> > > > @@ -501,7 +518,9 @@ 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_request_queues, nr_cpu_ids),
> > > > +            num_vqs);
> > > >         vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs),
> > > > GFP_KERNEL);
> > > >       if (!vblk->vqs)
> > > > -- 
> > > > 2.18.1