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

[Leon Romanovsky <leon@kernel.org>]

On Sun, Sep 05, 2021 at 11:15:16AM -0400, Michael S. Tsirkin wrote:
> On Sun, Sep 05, 2021 at 01:20:24PM +0300, Leon Romanovsky wrote:
> > On Sun, Sep 05, 2021 at 01:49:46AM -0700, Chaitanya Kulkarni wrote:
> > > 
> > > On 9/5/2021 12:46 AM, Leon Romanovsky wrote:
> > > > > +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");
> > > > > +
> > > > Won't it limit all virtio block devices to the same limit?
> > > > 
> > > > It is very common to see multiple virtio-blk devices on the same system
> > > > and they probably need different limits.
> > > > 
> > > > Thanks
> > > 
> > > 
> > > Without looking into the code, that can be done adding a configfs
> > > 
> > > interface and overriding a global value (module param) when it is set from
> > > 
> > > configfs.
> > 
> > So why should we do double work instead of providing one working
> > interface from the beginning?
> > 
> > Thanks
> > 
> > > 
> > > 
> 
> The main way to do it is really from the hypervisor. This one
> is a pretty blunt instrument, Max here says it's useful to reduce
> memory usage of the driver. If that's the usecase then a global limit
> seems sufficient.

How memory will you reduce? It is worth to write it in the commit message.

Thanks

> 
> -- 
> MST
>