Not all architectures and configurations define CPU topology information.

This can result in an empty topology directory in sysfs, and requires

in-kernel users to protect all uses with #ifdef - see

<http://marc.info/?l=linux-netdev&m=120639033904472&w=2>.
The documentation of CPU topology specifies what the defaults should be

if only partial information is available from the hardware.  So we can

provide these defaults as a fallback.
This patch:
- Adds default definitions of the 4 topology macros to

  include/asm-generic/topology.h.

- Changes include/asm-*/topology.h to include <asm-generic/topology.h>

  unconditionally.

- Changes drivers/base/topology.c to use the topology macros unconditionally

  and to cope with definitions that aren't lvalues.

- Updates documentation accordingly.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

diff --git a/Documentation/cputopology.txt b/Documentation/cputopology.txt

index b61cb95..c035481 100644

--- a/Documentation/cputopology.txt

+++ b/Documentation/cputopology.txt

@@ -14,9 +14,8 @@ represent the thread siblings to cpu X in the same physical package;

 To implement it in an architecture-neutral way, a new source file,

 drivers/base/topology.c, is to export the 4 attributes.
-If one architecture wants to support this feature, it just needs to

-implement 4 defines, typically in file include/asm-XXX/topology.h.

-The 4 defines are:

+If one architecture wants to support this feature, it must define

+some of these macros in include/asm-XXX/topology.h:

 #define topology_physical_package_id(cpu)

 #define topology_core_id(cpu)

 #define topology_thread_siblings(cpu)

@@ -25,17 +24,10 @@ The 4 defines are:

 The type of **_id is int.

 The type of siblings is cpumask_t.
-To be consistent on all architectures, the 4 attributes should have

-default values if their values are unavailable. Below is the rule.

-1) physical_package_id: If cpu has no physical package id, -1 is the

-default value.

-2) core_id: If...
[ message continues ]

I get a huuuuuuuge crash early in boot on the t61p dual x86_64 laptop.

Before netconsole has started and it has no serial port, so all I have is a

partially-scrolled-off jpg, sorry.
I'll drop the patch.
http://userweb.kernel.org/~akpm/p4175278.jpg

http://userweb.kernel.org/~akpm/config-t61p.txt

http://userweb.kernel.org/~akpm/dmesg-t61p.txt
If I didn't have all that wrong crap on the stack we'd have a full

trace here.  I have CONFIG_FRAME_POINTER=y, but that doesn't seem to

have helped.
--

<snip>
Damn, x86 is also using functions instead of macros.  Sorry about that; I'll

have another try.
Ben.
--

Ben Hutchings, Senior Software Engineer, Solarflare Communications

Not speaking for my employer; that's the marketing department's job.

--

ooh, I just discovered kstack=.  That should be hoisted up to core kernel

then pushed out to other architectures, not hidden in x86_64 code.
But first I guess it should be make to work - it fails miserably, because

only one of our seventy fix stack-dumping functions actually looks at it.
This:
--- a/arch/x86/kernel/traps_64.c~a

+++ a/arch/x86/kernel/traps_64.c

@@ -426,7 +426,7 @@ _show_stack(struct task_struct *tsk, str

 		printk(" %016lx", *stack++);

 		touch_nmi_watchdog();

 	}

-	show_trace(tsk, regs, sp, bp);

+//	show_trace(tsk, regs, sp, bp);

 }
 void show_stack(struct task_struct *tsk, unsigned long * sp)
works heaps better.
Here's the rest of your oops: http://userweb.kernel.org/~akpm/p4175279.jpg
I'd be suspecting startup ordering problems - maybe the page allocator

isn't ready yet.
otoh, it _should_ be ready by the time we run init_sched_domains().
--

powerpc allmodconfig:
arch/powerpc/kernel/pci_64.c:655: error: expected identifier or '(' before 'void'

arch/powerpc/kernel/pci_64.c:655: error: expected ')' before '(' token
Because this:
#ifdef CONFIG_NUMA

int pcibus_to_node(struct pci_bus *bus)

{

	struct pci_controller *phb = pci_bus_to_host(bus);

	return phb->node;

}

#endif
is expanding to
int ((void)(bus), -1)(struct pci_bus *bus)
which the compiler has trouble with.
This:
+++ a/include/asm-powerpc/topology.h

@@ -109,6 +109,8 @@ static inline void sysfs_remove_device_f

 #endif

 #endif
+#define pcibus_to_node pcibus_to_node

+

 #include <asm-generic/topology.h>
 #endif /* __KERNEL__ */

_
gets it working, by tricking the preprocessor into expanding pcibus_to_node

to itself, but it isn't exactly pleasing.
--

No, it isn't!  But cputopology.txt does say these should be macros, not

functions.
Ben.
--

Ben Hutchings, Senior Software Engineer, Solarflare Communications

Not speaking for my employer; that's the marketing department's job.

--

On Mon, 31 Mar 2008 12:44:13 +0100
I ran away in terror when I saw this patch.  It's dark and dirty stuff

you're unearthing there and it looks like a minefield of compilation

problems.  Not aided by the fact that we don't have a topology maintainer

afaik.  
We shall see.
--

i could pick it up into sched.git - it's a frequent party to topology

patches. We've now got automated cross-build checks as well by virtue of

Thomas so common build failures ought to be rare.
	Ingo

--

On Wed, 16 Apr 2008 14:51:33 +0200
OK, whatever.  There's a tangle between this change and the s390 tree which

already has a tangle with one of the sched-gits which is sort-of getting

sorted out.
git-s390 wasn't an appropriate place to host changes to

drivers/base/topology.c.
--

very nice - i suspect this would be a patch for -mm.
Acked-by: Ingo Molnar <mingo@elte.hu>
	Ingo

--