Re: [PATCH v4 5/5] nvdimm: Schedule device registration on node local to the device

[Alexander Duyck]

On 9/20/2018 3:59 PM, Dan Williams wrote:
> On Thu, Sep 20, 2018 at 3:31 PM Alexander Duyck
> <alexander.h.duyck@xxxxxxxxxxxxxxx> wrote:
> > This patch is meant to force the device registration for nvdimm devices to
> > be closer to the actual device. This is achieved by using either the NUMA
> > node ID of the region, or of the parent. By doing this we can have
> > everything above the region based on the region, and everything below the
> > region based on the nvdimm bus.
> >
> > One additional change I made is that we hold onto a reference to the parent
> > while we are going through registration. By doing this we can guarantee we
> > can complete the registration before we have the parent device removed.
> >
> > By guaranteeing NUMA locality I see an improvement of as high as 25% for
> > per-node init of a system with 12TB of persistent memory.
> >
> > Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/nvdimm/bus.c |   19 +++++++++++++++++--
> >   1 file changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c
> > index 8aae6dcc839f..ca935296d55e 100644
> > --- a/drivers/nvdimm/bus.c
> > +++ b/drivers/nvdimm/bus.c
> > @@ -487,7 +487,9 @@ static void nd_async_device_register(void *d, async_cookie_t cookie)
> >                  dev_err(dev, "%s: failed\n", __func__);
> >                  put_device(dev);
> >          }
> > +
> >          put_device(dev);
> > +       put_device(dev->parent);
>
> Good catch. The child does not pin the parent until registration, but
> we need to make sure the parent isn't gone while were waiting for the
> registration work to run.
>
> Let's break this reference count fix out into its own separate patch,
> because this looks to be covering a gap that may need to be
> recommended for -stable.

Okay, I guess I can do that.

> >   static void nd_async_device_unregister(void *d, async_cookie_t cookie)
> > @@ -504,12 +506,25 @@ static void nd_async_device_unregister(void *d, async_cookie_t cookie)
> >
> >   void __nd_device_register(struct device *dev)
> >   {
> > +       int node;
> > +
> >          if (!dev)
> >                  return;
> > +
> >          dev->bus = &nvdimm_bus_type;
> > +       get_device(dev->parent);
> >          get_device(dev);
> > -       async_schedule_domain(nd_async_device_register, dev,
> > -                       &nd_async_domain);
> > +
> > +       /*
> > +        * For a region we can break away from the parent node,
> > +        * otherwise for all other devices we just inherit the node from
> > +        * the parent.
> > +        */
> > +       node = is_nd_region(dev) ? to_nd_region(dev)->numa_node :
> > +                                  dev_to_node(dev->parent);
>
> Devices already automatically inherit the node of their parent, so I'm
> not understanding why this is needed?

That doesn't happen until you call device_add, which you don't call 
until nd_async_device_register. All that has been called on the device 
up to now is device_initialize which leaves the node at NUMA_NO_NODE.