linux-kernel - Re: [PATCH v2 2/9] x86: numa: check the node id consistently for x86

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Date:   Mon, 2 Sep 2019 21:14:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>, dalias@...c.org,
        linux-sh@...r.kernel.org, catalin.marinas@....com,
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        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
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Subject: Re: [PATCH v2 2/9] x86: numa: check the node id consistently for x86

On Mon, Sep 02, 2019 at 08:22:52PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:

> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index f0dd8e38fee3..2caf204966a0 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -2120,8 +2120,16 @@ int device_add(struct device *dev)
> >  		dev->kobj.parent = kobj;
> >  
> >  	/* use parent numa_node */
> > -	if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
> > -		set_dev_node(dev, dev_to_node(parent));
> > +	if (dev_to_node(dev) == NUMA_NO_NODE) {
> > +		if (parent)
> > +			set_dev_node(dev, dev_to_node(parent));
> > +#ifdef CONFIG_NUMA
> > +		else {
> > +			pr_err("device: '%s': has no assigned NUMA node\n", dev_name(dev));
> > +			set_dev_node(dev, 0);
> > +		}
> > +#endif
> 
> BTW., is firmware required to always provide a NUMA node on NUMA systems?
> 
> I.e. do we really want this warning on non-NUMA systems that don't assign 
> NUMA nodes?

Good point; we might have to exclude nr_node_ids==1 systems from
warning.

> Also, even on NUMA systems, is firmware required to provide a NUMA node - 
> i.e. is it in principle invalid to offer no NUMA binding?

I think so; a device needs to be _somewhere_, right? Typically though;
devices are on a PCI bus, and the PCI bridge itself will have a NUMA
binding and then the above parent rule will make everything just work.

But I don't see how you can be outside of the NUMA topology.