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This patch:

- implements per-architecture NR_CPUS value with a default value
that is the maximum per-arch (e.g. BITS_PER_LONG).

- provides a configure option for changing the value.

Setting a saner NR_CPUS, e.g. 2, reduced my kernel footprint by over
200KB (all in data and bss). Now that we have loops terminating on
NR_CPUS, you can save a bit of cycles too.

Patch is against 2.5.32...

Robert Love

diff -urN linux-2.5.32/arch/alpha/config.in linux/arch/alpha/config.in
--- linux-2.5.32/arch/alpha/config.in Tue Aug 27 15:26:37 2002
+++ linux/arch/alpha/config.in Wed Aug 28 19:15:32 2002
@@ -233,6 +233,7 @@

if [ "$CONFIG_SMP" = "y" ]; then
define_bool CONFIG_HAVE_DEC_LOCK y
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
fi

if [ "$CONFIG_EXPERIMENTAL" = "y" ]; then
diff -urN linux-2.5.32/arch/i386/Config.help linux/arch/i386/Config.help
--- linux-2.5.32/arch/i386/Config.help Tue Aug 27 15:26:34 2002
+++ linux/arch/i386/Config.help Wed Aug 28 19:15:32 2002
@@ -25,6 +25,14 @@

If you don't know what to do here, say N.

+CONFIG_NR_CPUS
+ This allows you to specify the maximum number of CPUs which this
+ kernel will support. The maximum supported value is 32 and the
+ minimum value which makes sense is 2.
+
+ This is purely to save memory - each supported CPU adds
+ approximately eight kilobytes to the kernel image.
+
CONFIG_PREEMPT
This option reduces the latency of the kernel when reacting to
real-time or interactive events by allowing a low priority process to
diff -urN linux-2.5.32/arch/i386/config.in linux/arch/i386/config.in
--- linux-2.5.32/arch/i386/config.in Tue Aug 27 15:26:39 2002
+++ linux/arch/i386/config.in Wed Aug 28 19:15:32 2002
@@ -166,6 +166,7 @@
define_bool CONFIG_X86_IO_APIC y
fi
else
+ int 'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
bool 'Multiquad NUMA system' CONFIG_MULTIQUAD
fi

diff -urN linux-2.5.32/arch/i386/defconfig linux/arch/i386/defconfig
--- linux-2.5.32/arch/i386/defconfig Tue Aug 27 15:26:34 2002
+++ linux/arch/i386/defconfig Wed Aug 28 19:15:32 2002
@@ -75,6 +75,7 @@
# CONFIG_MATH_EMULATION is not set
# CONFIG_MTRR is not set
CONFIG_HAVE_DEC_LOCK=y
+CONFIG_NR_CPUS=32

#
# Power management options (ACPI, APM)
diff -urN linux-2.5.32/arch/ia64/config.in linux/arch/ia64/config.in
--- linux-2.5.32/arch/ia64/config.in Tue Aug 27 15:27:34 2002
+++ linux/arch/ia64/config.in Wed Aug 28 19:15:32 2002
@@ -96,6 +96,10 @@
tristate '/proc/pal support' CONFIG_IA64_PALINFO
tristate '/proc/efi/vars support' CONFIG_EFI_VARS

+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
+fi
+
tristate 'Kernel support for ELF binaries' CONFIG_BINFMT_ELF
tristate 'Kernel support for MISC binaries' CONFIG_BINFMT_MISC

diff -urN linux-2.5.32/arch/ia64/defconfig linux/arch/ia64/defconfig
--- linux-2.5.32/arch/ia64/defconfig Tue Aug 27 15:26:34 2002
+++ linux/arch/ia64/defconfig Wed Aug 28 19:15:32 2002
@@ -61,6 +61,7 @@
CONFIG_EFI_VARS=y
CONFIG_BINFMT_ELF=y
# CONFIG_BINFMT_MISC is not set
+CONFIG_NR_CPUS=64

#
# ACPI Support
diff -urN linux-2.5.32/arch/mips/config.in linux/arch/mips/config.in
--- linux-2.5.32/arch/mips/config.in Tue Aug 27 15:26:53 2002
+++ linux/arch/mips/config.in Wed Aug 28 19:15:32 2002
@@ -490,6 +490,8 @@
bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
if [ "$CONFIG_SMP" != "y" ]; then
bool 'Run uncached' CONFIG_MIPS_UNCACHED
+else
+ int 'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
fi
endmenu

diff -urN linux-2.5.32/arch/mips64/config.in linux/arch/mips64/config.in
--- linux-2.5.32/arch/mips64/config.in Tue Aug 27 15:26:35 2002
+++ linux/arch/mips64/config.in Wed Aug 28 19:15:32 2002
@@ -244,6 +244,8 @@
bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
if [ "$CONFIG_SMP" != "y" ]; then
bool 'Run uncached' CONFIG_MIPS_UNCACHED
+else
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
fi
endmenu

diff -urN linux-2.5.32/arch/mips64/defconfig linux/arch/mips64/defconfig
--- linux-2.5.32/arch/mips64/defconfig Tue Aug 27 15:26:37 2002
+++ linux/arch/mips64/defconfig Wed Aug 28 19:15:32 2002
@@ -32,6 +32,7 @@
# CONFIG_EISA is not set
# CONFIG_MCA is not set
# CONFIG_SBUS is not set
+CONFIG_NR_CPUS=64

#
# CPU selection
diff -urN linux-2.5.32/arch/parisc/config.in linux/arch/parisc/config.in
--- linux-2.5.32/arch/parisc/config.in Tue Aug 27 15:27:33 2002
+++ linux/arch/parisc/config.in Wed Aug 28 19:15:32 2002
@@ -19,6 +19,10 @@
# bool 'Symmetric multi-processing support' CONFIG_SMP
define_bool CONFIG_SMP n

+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
+fi
+
bool 'Kernel Debugger support' CONFIG_KWDB
# define_bool CONFIG_KWDB n

diff -urN linux-2.5.32/arch/ppc/config.in linux/arch/ppc/config.in
--- linux-2.5.32/arch/ppc/config.in Tue Aug 27 15:26:30 2002
+++ linux/arch/ppc/config.in Wed Aug 28 19:15:32 2002
@@ -173,6 +173,7 @@
bool 'Symmetric multi-processing support' CONFIG_SMP
if [ "$CONFIG_SMP" = "y" ]; then
bool ' Distribute interrupts on all CPUs by default' CONFIG_IRQ_ALL_CPUS
+ int 'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
fi
if [ "$CONFIG_SMP" != "y" ]; then
bool 'Preemptible Kernel' CONFIG_PREEMPT
diff -urN linux-2.5.32/arch/ppc64/config.in linux/arch/ppc64/config.in
--- linux-2.5.32/arch/ppc64/config.in Tue Aug 27 15:26:35 2002
+++ linux/arch/ppc64/config.in Wed Aug 28 19:15:32 2002
@@ -21,6 +21,7 @@
bool 'Symmetric multi-processing support' CONFIG_SMP
if [ "$CONFIG_SMP" = "y" ]; then
bool ' Distribute interrupts on all CPUs by default' CONFIG_IRQ_ALL_CPUS
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
if [ "$CONFIG_PPC_PSERIES" = "y" ]; then
bool ' Hardware multithreading' CONFIG_HMT
bool ' Discontiguous Memory Support' CONFIG_DISCONTIGMEM
diff -urN linux-2.5.32/arch/ppc64/defconfig linux/arch/ppc64/defconfig
--- linux-2.5.32/arch/ppc64/defconfig Tue Aug 27 15:26:38 2002
+++ linux/arch/ppc64/defconfig Wed Aug 28 19:15:55 2002
@@ -39,6 +39,7 @@
# CONFIG_HMT is not set
# CONFIG_DISCONTIGMEM is not set
# CONFIG_PREEMPT is not set
+CONFIG_NR_CPUS=64
# CONFIG_RTAS_FLASH is not set

#
diff -urN linux-2.5.32/arch/s390/config.in linux/arch/s390/config.in
--- linux-2.5.32/arch/s390/config.in Tue Aug 27 15:26:37 2002
+++ linux/arch/s390/config.in Wed Aug 28 19:15:32 2002
@@ -20,6 +20,9 @@
comment 'Processor type and features'
bool 'Symmetric multi-processing support' CONFIG_SMP
bool 'IEEE FPU emulation' CONFIG_MATHEMU
+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
+fi
endmenu

mainmenu_option next_comment
diff -urN linux-2.5.32/arch/s390/defconfig linux/arch/s390/defconfig
--- linux-2.5.32/arch/s390/defconfig Tue Aug 27 15:27:12 2002
+++ linux/arch/s390/defconfig Wed Aug 28 19:15:32 2002
@@ -35,6 +35,7 @@
#
CONFIG_SMP=y
CONFIG_MATHEMU=y
+CONFIG_NR_CPUS=64

#
# Base setup
diff -urN linux-2.5.32/arch/s390x/config.in linux/arch/s390x/config.in
--- linux-2.5.32/arch/s390x/config.in Tue Aug 27 15:26:34 2002
+++ linux/arch/s390x/config.in Wed Aug 28 19:15:32 2002
@@ -19,6 +19,9 @@
mainmenu_option next_comment
comment 'Processor type and features'
bool 'Symmetric multi-processing support' CONFIG_SMP
+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
+fi
bool 'Kernel support for 31 bit emulation' CONFIG_S390_SUPPORT
if [ "$CONFIG_S390_SUPPORT" = "y" ]; then
tristate 'Kernel support for 31 bit ELF binaries' CONFIG_BINFMT_ELF32
diff -urN linux-2.5.32/arch/s390x/defconfig linux/arch/s390x/defconfig
--- linux-2.5.32/arch/s390x/defconfig Tue Aug 27 15:26:30 2002
+++ linux/arch/s390x/defconfig Wed Aug 28 19:15:32 2002
@@ -36,6 +36,7 @@
CONFIG_SMP=y
CONFIG_S390_SUPPORT=y
CONFIG_BINFMT_ELF32=y
+CONFIG_NR_CPUS=64

#
# Base setup
diff -urN linux-2.5.32/arch/sparc/config.in linux/arch/sparc/config.in
--- linux-2.5.32/arch/sparc/config.in Tue Aug 27 15:26:33 2002
+++ linux/arch/sparc/config.in Wed Aug 28 19:15:32 2002
@@ -18,6 +18,10 @@

bool 'Symmetric multi-processing support (does not work on sun4/sun4c)' CONFIG_SMP

+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
+fi
+
# Identify this as a Sparc32 build
define_bool CONFIG_SPARC32 y

diff -urN linux-2.5.32/arch/sparc64/config.in linux/arch/sparc64/config.in
--- linux-2.5.32/arch/sparc64/config.in Tue Aug 27 15:26:39 2002
+++ linux/arch/sparc64/config.in Wed Aug 28 19:15:32 2002
@@ -17,6 +17,10 @@
bool 'Symmetric multi-processing support' CONFIG_SMP
bool 'Preemptible Kernel' CONFIG_PREEMPT

+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
+fi
+
# Identify this as a Sparc64 build
define_bool CONFIG_SPARC64 y

diff -urN linux-2.5.32/arch/sparc64/defconfig linux/arch/sparc64/defconfig
--- linux-2.5.32/arch/sparc64/defconfig Tue Aug 27 15:26:39 2002
+++ linux/arch/sparc64/defconfig Wed Aug 28 19:15:32 2002
@@ -57,6 +57,7 @@
CONFIG_BINFMT_MISC=m
# CONFIG_SUNOS_EMUL is not set
CONFIG_SOLARIS_EMUL=m
+CONFIG_NR_CPUS=64

#
# Parallel port support
diff -urN linux-2.5.32/arch/x86_64/config.in linux/arch/x86_64/config.in
--- linux-2.5.32/arch/x86_64/config.in Tue Aug 27 15:26:37 2002
+++ linux/arch/x86_64/config.in Wed Aug 28 19:15:32 2002
@@ -54,6 +54,7 @@
fi
if [ "$CONFIG_SMP" = "y" ]; then
define_bool CONFIG_HAVE_DEC_LOCK y
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
fi

define_bool CONFIG_X86_MCE y
diff -urN linux-2.5.32/arch/x86_64/defconfig linux/arch/x86_64/defconfig
--- linux-2.5.32/arch/x86_64/defconfig Tue Aug 27 15:26:54 2002
+++ linux/arch/x86_64/defconfig Wed Aug 28 19:15:32 2002
@@ -51,6 +51,7 @@
CONFIG_HAVE_DEC_LOCK=y
CONFIG_X86_MCE=y
# CONFIG_X86_MCE_NONFATAL is not set
+CONFIG_NR_CPUS=64

#
# Power management options
diff -urN linux-2.5.32/include/linux/threads.h linux/include/linux/threads.h
--- linux-2.5.32/include/linux/threads.h Tue Aug 27 15:26:32 2002
+++ linux/include/linux/threads.h Wed Aug 28 19:15:32 2002
@@ -8,10 +8,16 @@
* /proc/sys/kernel/threads-max.
*/

+/*
+ * Maximum supported processors that can run under SMP. This value is
+ * set via configure setting. The maximum is equal to the size of the
+ * bitmasks used on that platform, i.e. 32 or 64. Setting this smaller
+ * saves quite a bit of memory.
+ */
#ifdef CONFIG_SMP
-#define NR_CPUS 32 /* Max processors that can be running in SMP */
+#define NR_CPUS CONFIG_NR_CPUS
#else
-#define NR_CPUS 1
+#define NR_CPUS 1
#endif

#define MIN_THREADS_LEFT_FOR_ROOT 4
-
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