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powerpc: Make the NR_CPUS max 8192

PATCH In review Michael Neuling 3 participants 5 messages May 18, 2009 PowerPC

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Michael Neuling

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#0 lore raw

PATCH 1/1 powerpc: Make the NR_CPUS max 8192

We can compile and boot with NR_CPUS=8192, so make this the max. 1024 was an arbitrary decision anyway.

Signed-off-by Michael Neuling <[email protected]>

--
No, I've not actually booted on a 8192 way machine, although if wishing made it so....

 arch/powerpc/platforms/Kconfig.cputype |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
arch/powerpc/platforms/Kconfig.cputype +2 -2
Index: linux-2.6-ozlabs/arch/powerpc/platforms/Kconfig.cputype
===================================================================
@@ -262,8 +262,8 @@ config SMP
 	  If you don't know what to do here, say N.
 
 config NR_CPUS
-	int "Maximum number of CPUs (2-1024)"
-	range 2 1024
+	int "Maximum number of CPUs (2-8192)"
+	range 2 8192
 	depends on SMP
 	default "32" if PPC64
 	default "4"
#1 lore raw
Quoted 2 lines · Michael Neuling

We can compile and boot with NR_CPUS=8192, so make this the max. 1024 was an arbitrary decision anyway.

Is 8192 still arbitrary? Or does something break above that?

cheers

author
#2 lore raw
Quoted 4 lines
Quoted 2 lines

We can compile and boot with NR_CPUS=3D8192, so make this the max. 1024 was an arbitrary decision anyway.

Is 8192 still arbitrary? Or does something break above that?

Yeah, the compile breaks after that with 4K pages.

In drivers/base/node.c we have:

	/* 2008/04/07: buf currently PAGE_SIZE, need 9 chars per 32 bits. */
	BUILD_BUG_ON((NR_CPUS/32 * 9) > (PAGE_SIZE-1));

which causes:
drivers/base/node.c: In function 'node_read_cpumap':
drivers/base/node.c:31: error: size of array 'type name' is negative

I can compile with 16384 CPUs with 64K pages, but it doesn't boot.

sfr asked for size info for different builds, so I may as well repost them here:

text data bss dec hex filename
9237767 3225768 4409996 16873531 101783b vmlinux.1024
9247355 4769472 7373708 21390535 14664c7 vmlinux.2048
9267239 7857032 13301132 30425403 1d0413b vmlinux.4096
9302623 14035832 25155980 48494435 2e3f763 vmlinux.8192
9373283 26389360 48865676 84628319 50b535f vmlinux.16384

config was pseries_defconfig but with 64K pages.

Mikey

#3 lore raw
Quoted 19 lines · Michael Neuling
Quoted 4 lines
Quoted 2 lines

We can compile and boot with NR_CPUS=3D8192, so make this the max. 1024 was an arbitrary decision anyway.

Is 8192 still arbitrary? Or does something break above that?

Yeah, the compile breaks after that with 4K pages.

In drivers/base/node.c we have:

	/* 2008/04/07: buf currently PAGE_SIZE, need 9 chars per 32 bits. */
	BUILD_BUG_ON((NR_CPUS/32 * 9) > (PAGE_SIZE-1));

which causes:
drivers/base/node.c: In function 'node_read_cpumap':
drivers/base/node.c:31: error: size of array 'type name' is negative

I can compile with 16384 CPUs with 64K pages, but it doesn't boot.

sfr asked for size info for different builds, so I may as well repost them here:

Quoted 6 lines

text data bss dec hex filename
9237767 3225768 4409996 16873531 101783b vmlinux.1024
9247355 4769472 7373708 21390535 14664c7 vmlinux.2048
9267239 7857032 13301132 30425403 1d0413b vmlinux.4096
9302623 14035832 25155980 48494435 2e3f763 vmlinux.8192
9373283 26389360 48865676 84628319 50b535f vmlinux.16384

Will distros now start pushing NR_CPUS=8192-kernels on us?

With kind regards,

Geert Uytterhoeven
Software Architect
Techsoft Centre

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author
#4 lore raw
Quoted 2 lines · In message <[email protected]> you wrote:
Quoted 1 line · Michael Neuling
Quoted 1 line
Quoted 1 line

We can compile and boot with NR_CPUS=3D8192, so make this the max. 102

4

Quoted 13 lines
Quoted 13 lines
Quoted 3 lines
Quoted 1 line

was an arbitrary decision anyway.

Is 8192 still arbitrary? Or does something break above that?

Yeah, the compile breaks after that with 4K pages.

In drivers/base/node.c we have:

	/* 2008/04/07: buf currently PAGE_SIZE, need 9 chars per 32 bits. */
	BUILD_BUG_ON((NR_CPUS/32 * 9) > (PAGE_SIZE-1));

which causes:
drivers/base/node.c: In function 'node_read_cpumap':
drivers/base/node.c:31: error: size of array 'type name' is negative

Quoted 6 lines
Quoted 6 lines

I can compile with 16384 CPUs with 64K pages, but it doesn't boot.

sfr asked for size info for different builds, so I may as well repost them here:

text data bss dec hex filenam

e

Quoted 1 line
Quoted 1 line

9237767 3225768 4409996 16873531 101783b vmlinux

.1024

Quoted 1 line
Quoted 1 line

9247355 4769472 7373708 21390535 14664c7 vmlinux

.2048

Quoted 1 line
Quoted 1 line

9267239 7857032 13301132 30425403 1d0413b vmlinux

.4096

Quoted 1 line
Quoted 1 line

9302623 14035832 25155980 48494435 2e3f763 vmlinux

.8192

Quoted 1 line
Quoted 1 line

9373283 26389360 48865676 84628319 50b535f vmlinux

.16384

Quoted 2 lines

Will distros now start pushing NR_CPUS=8192-kernels on us?

Yeah, that's a concern.

Mikey