linux-kernel - Re: [PATCH] x86 Topology cpu_to

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Date:	Fri, 3 Oct 2008 13:21:43 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Steven Rostedt <rostedt@...dmis.org>, colpatch@...ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jonathan Corbet <corbet@....net>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com, "Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH] x86 Topology cpu_to_node parameter check

* Steven Rostedt (rostedt@...dmis.org) wrote:
> 
> On Fri, 3 Oct 2008, Mathieu Desnoyers wrote:
> > 
> > That's how I did it first, but then I looked at asm-generic/topology.h
> > and have seen it uses #defines. Should we change them too ?
> > 
> 
> The old way of doing this is with defines. But all new code should be 
> static inline functions when feasible. This way we can get typechecking 
> on the parameters even when the configuration is disabled.
> 
> Even if the rest of the file uses defines, the new code should be
> static inlines. Eventually, even the old defines will be converted.
> 
> -- Steve
> 

Argh, I think topology.h is utterly broken :-(

Have you noticed the subtile interaction between the

include/asm-x86/topology.h :

#define numa_node_id()          0
#define cpu_to_node(cpu)        0
#define early_cpu_to_node(cpu)  0
...
#include <asm-generic/topology.h>


and
include/asm-generic/topology.h :
#ifndef cpu_to_node
#define cpu_to_node(cpu)        ((void)(cpu),0)
#endif

If any architecture decide for some reason to use a static inline rather
than a define, as currently done with node_to_first_cpu :

include/asm-x86/topology.h :
static inline int node_to_first_cpu(int node)
{
        return first_cpu(cpu_online_map);
}
...
#include <asm-generic/topology.h>

include/asm-generic/topology.h :
#ifndef node_to_first_cpu
#define node_to_first_cpu(node) ((void)(node),0)
#endif

(which will override the static inline !)

It results in an override of the arch-specific version. Nice eh ?

Mathieu

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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