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From: Peter Zijlstra <peterz@infradead.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Rich Felker <dalias@libc.org>,
	Linux-sh list <linux-sh@vger.kernel.org>,
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	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware
Date: Thu, 26 Sep 2019 14:24:06 +0200
Message-ID: <20190926122406.GB4519@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAMuHMdVJ6RbEbKc8s_rhJaUBNnA8sOByq9cJ3KH-qmcqQrm_UQ@mail.gmail.com>

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 <peterz@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.

      reply index

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-17 12:48 Yunsheng Lin
2019-09-21 22:38 ` Paul Burton
2019-09-23  2:31   ` Yunsheng Lin
2019-09-23 15:15 ` Peter Zijlstra
2019-09-23 15:28   ` Michal Hocko
2019-09-23 15:48     ` Peter Zijlstra
2019-09-23 16:52       ` Michal Hocko
2019-09-23 20:34         ` Peter Zijlstra
2019-09-24  1:29           ` Yunsheng Lin
2019-09-24  9:25             ` Peter Zijlstra
2019-09-24 11:07               ` Yunsheng Lin
2019-09-24 11:28                 ` Peter Zijlstra
2019-09-24 11:44                   ` Yunsheng Lin
2019-09-24 11:58                     ` Peter Zijlstra
2019-09-24 12:09                       ` Yunsheng Lin
2019-09-24  7:47           ` Michal Hocko
2019-09-24  9:17             ` Peter Zijlstra
2019-09-24 10:56               ` Michal Hocko
2019-09-24 11:23                 ` Peter Zijlstra
2019-09-24 11:54                   ` Michal Hocko
2019-09-24 12:09                     ` Peter Zijlstra
2019-09-24 12:25                       ` Michal Hocko
2019-09-24 12:43                         ` Peter Zijlstra
2019-09-24 12:59                           ` Peter Zijlstra
2019-09-24 13:19                             ` Michal Hocko
2019-09-25  9:14                               ` Yunsheng Lin
2019-09-25 10:41                                 ` Peter Zijlstra
2019-10-08  8:38                                   ` Yunsheng Lin
2019-10-09 12:25                                     ` Robin Murphy
2019-10-10  6:07                                       ` Yunsheng Lin
2019-10-10  7:32                                         ` Michal Hocko
2019-10-11  3:27                                           ` Yunsheng Lin
2019-10-11 11:15                                             ` Peter Zijlstra
2019-10-12  6:17                                               ` Yunsheng Lin
2019-10-12  7:40                                                 ` Greg KH
2019-10-12  9:47                                                   ` Yunsheng Lin
2019-10-12 10:40                                                     ` Greg KH
2019-10-12 10:47                                                       ` Greg KH
2019-10-14  8:00                                                         ` Yunsheng Lin
2019-10-14  9:25                                                           ` Greg KH
2019-10-14  9:49                                                             ` Peter Zijlstra
2019-10-14 10:04                                                               ` Greg KH
2019-10-15 10:40                                                             ` Yunsheng Lin
2019-10-15 16:58                                                               ` Greg KH
2019-10-16 12:07                                                                 ` Yunsheng Lin
2019-10-28  9:20                                                   ` Yunsheng Lin
2019-10-29  8:53                                                     ` Michal Hocko
2019-10-30  1:58                                                       ` Yunsheng Lin
2019-10-10  8:56                                       ` Peter Zijlstra
2019-09-25 10:40                               ` Peter Zijlstra
2019-09-25 13:25                                 ` Michal Hocko
2019-09-25 16:31                                   ` Peter Zijlstra
2019-09-25 21:45                                     ` Peter Zijlstra
2019-09-26  9:05                                       ` Peter Zijlstra
2019-09-26 12:10                                         ` Peter Zijlstra
2019-09-26 11:45                                     ` Geert Uytterhoeven
2019-09-26 12:24                                       ` Peter Zijlstra [this message]

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