Linux Virtualization - Sep 2021 - [PATCH v3 1/1] virtio-blk: add num_request_queues module parameter

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
> 
>

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.

-- 
MST