On Thu, Sep 26, 2019 at 01:45:53PM +0200, Geert Uytterhoeven wrote: > Hi Peter, > > On Thu, Sep 26, 2019 at 11:42 AM Peter Zijlstra <pet...@infradead.org> wrote: > > On Wed, Sep 25, 2019 at 03:25:44PM +0200, Michal Hocko wrote: > > > I am sorry but I still do not understand why you consider this whack a > > > mole better then simply live with the fact that NUMA_NO_NODE is a > > > reality and that using the full cpu mask is a reasonable answer to that. > > > > Because it doesn't make physical sense. A device _cannot_ be local to > > all CPUs in a NUMA system. > > While it cannot be local to all CPUs, it can be at a uniform (equal) distance > to each CPU node, can't it?
Only in some really narrow cases; and I'm not sure those are realistic, nor if then not providing NUMA info is the best way to describe that. I suppose it is possible to have a PCI bridge shared between two nodes, such that the PCI devices have equidistance; esp. if that all lives in a package. But the moment you scale this out, you either get devices that are 'local' to a package while having multiple packages, or if you maintain a single bridge in a big system, things become so slow it all doesn't matter anyway (try having a equidistant device in a 16 node system). I'm saying that assigning a node (one of the shared) is, in the generic ase of multiple packages, the better solution over assigning all nodes. The other solution is migrating the device model over to a node mask, instead of a single node. But like said; I'm not sure anybody actually build something like this. So I'm not sure it matters. OTOH allowing to not describe NUMA has led to a whole host of crap, which if we don't become stricter will only get worse.
