This patch implements a CONFIG_NR_CPUS that allows the user to specify a
sane value for NR_CPUS in an effort to save memory and cycles. This is
especially useful for debugging or other work where you have large
per-CPU static structures. It also has a more appreciable benefit now
that hotplug CPUs has more code using NR_CPUS vs smp_num_cpus.
This patch also allows each architecture to specify its own default
NR_CPUS, allowing 64-bit arches to set their default to 64.
We need feedback on use of other-than-default NR_CPUS values (x86 is
well tested) as well as use of the new 64 default on such architectures.
Oh, and to make Tom Rini happy I will accept patches for other
architectures Config.help entries :)
Patch is against 2.5.24.
Robert Love
diff -urN linux-2.5.24/arch/alpha/config.in linux/arch/alpha/config.in
--- linux-2.5.24/arch/alpha/config.in Thu Jun 20 15:53:47 2002
+++ linux/arch/alpha/config.in Thu Jun 20 16:35:45 2002
@@ -232,6 +232,7 @@
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-2.5.24/arch/i386/Config.help linux/arch/i386/Config.help
--- linux-2.5.24/arch/i386/Config.help Thu Jun 20 15:53:44 2002
+++ linux/arch/i386/Config.help Thu Jun 20 16:35:45 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-2.5.24/arch/i386/config.in linux/arch/i386/config.in
--- linux-2.5.24/arch/i386/config.in Thu Jun 20 15:53:49 2002
+++ linux/arch/i386/config.in Thu Jun 20 16:35:45 2002
@@ -165,6 +165,7 @@
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-2.5.24/arch/i386/defconfig linux/arch/i386/defconfig
--- linux-2.5.24/arch/i386/defconfig Thu Jun 20 15:53:45 2002
+++ linux/arch/i386/defconfig Thu Jun 20 16:35:45 2002
@@ -74,6 +74,7 @@
# CONFIG_PREEMPT is not set
# CONFIG_MULTIQUAD is not set
CONFIG_HAVE_DEC_LOCK=y
+CONFIG_NR_CPUS=32
#
# General options
diff -urN linux-2.5.24/arch/ia64/config.in linux/arch/ia64/config.in
--- linux-2.5.24/arch/ia64/config.in Thu Jun 20 15:53:53 2002
+++ linux/arch/ia64/config.in Thu Jun 20 16:35:45 2002
@@ -95,6 +95,10 @@
tristate '/proc/pal support' CONFIG_IA64_PALINFO
tristate '/proc/efi/vars support' CONFIG_EFI_VARS
+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
+fi
+
tristate 'Kernel support for ELF binaries' CONFIG_BINFMT_ELF
tristate 'Kernel support for MISC binaries' CONFIG_BINFMT_MISC
diff -urN linux-2.5.24/arch/ia64/defconfig linux/arch/ia64/defconfig
--- linux-2.5.24/arch/ia64/defconfig Thu Jun 20 15:53:44 2002
+++ linux/arch/ia64/defconfig Thu Jun 20 16:35:45 2002
@@ -61,6 +61,7 @@
CONFIG_EFI_VARS=y
CONFIG_BINFMT_ELF=y
# CONFIG_BINFMT_MISC is not set
+CONFIG_NR_CPUS=64
#
# ACPI Support
diff -urN linux-2.5.24/arch/mips/config.in linux/arch/mips/config.in
--- linux-2.5.24/arch/mips/config.in Thu Jun 20 15:53:54 2002
+++ linux/arch/mips/config.in Thu Jun 20 16:35:45 2002
@@ -500,6 +500,8 @@
bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
if [ "$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-2.5.24/arch/mips64/config.in linux/arch/mips64/config.in
--- linux-2.5.24/arch/mips64/config.in Thu Jun 20 15:53:45 2002
+++ linux/arch/mips64/config.in Thu Jun 20 16:35:45 2002
@@ -245,6 +245,8 @@
bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
if [ "$CONFIG_SMP" != "y" ]; then
bool 'Run uncached' CONFIG_MIPS_UNCACHED
+else
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
fi
endmenu
diff -urN linux-2.5.24/arch/mips64/defconfig linux/arch/mips64/defconfig
--- linux-2.5.24/arch/mips64/defconfig Thu Jun 20 15:53:47 2002
+++ linux/arch/mips64/defconfig Thu Jun 20 16:35:45 2002
@@ -32,6 +32,7 @@
# CONFIG_EISA is not set
# CONFIG_MCA is not set
# CONFIG_SBUS is not set
+CONFIG_NR_CPUS=64
#
# CPU selection
diff -urN linux-2.5.24/arch/parisc/config.in linux/arch/parisc/config.in
--- linux-2.5.24/arch/parisc/config.in Thu Jun 20 15:53:57 2002
+++ linux/arch/parisc/config.in Thu Jun 20 16:35:45 2002
@@ -18,6 +18,10 @@
# bool 'Symmetric multi-processing support' CONFIG_SMP
define_bool CONFIG_SMP n
+if [ "$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-2.5.24/arch/ppc/config.in linux/arch/ppc/config.in
--- linux-2.5.24/arch/ppc/config.in Thu Jun 20 15:53:41 2002
+++ linux/arch/ppc/config.in Thu Jun 20 16:35:45 2002
@@ -172,6 +172,7 @@
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-2.5.24/arch/ppc64/config.in linux/arch/ppc64/config.in
--- linux-2.5.24/arch/ppc64/config.in Thu Jun 20 15:53:45 2002
+++ linux/arch/ppc64/config.in Thu Jun 20 16:35:45 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
fi
diff -urN linux-2.5.24/arch/ppc64/defconfig linux/arch/ppc64/defconfig
--- linux-2.5.24/arch/ppc64/defconfig Thu Jun 20 15:53:48 2002
+++ linux/arch/ppc64/defconfig Thu Jun 20 16:35:45 2002
@@ -38,6 +38,7 @@
CONFIG_IRQ_ALL_CPUS=y
# CONFIG_HMT is not set
# CONFIG_PREEMPT is not set
+CONFIG_NR_CPUS=64
#
# General setup
diff -urN linux-2.5.24/arch/s390/config.in linux/arch/s390/config.in
--- linux-2.5.24/arch/s390/config.in Thu Jun 20 15:53:47 2002
+++ linux/arch/s390/config.in Thu Jun 20 16:35:45 2002
@@ -20,6 +20,9 @@
comment 'Processor type and features'
bool 'Symmetric multi-processing support' CONFIG_SMP
bool 'IEEE FPU emulation' CONFIG_MATHEMU
+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
+fi
endmenu
mainmenu_option next_comment
diff -urN linux-2.5.24/arch/s390/defconfig linux/arch/s390/defconfig
--- linux-2.5.24/arch/s390/defconfig Thu Jun 20 15:53:56 2002
+++ linux/arch/s390/defconfig Thu Jun 20 16:35:45 2002
@@ -35,6 +35,7 @@
#
CONFIG_SMP=y
CONFIG_MATHEMU=y
+CONFIG_NR_CPUS=64
#
# Base setup
diff -urN linux-2.5.24/arch/s390x/config.in linux/arch/s390x/config.in
--- linux-2.5.24/arch/s390x/config.in Thu Jun 20 15:53:44 2002
+++ linux/arch/s390x/config.in Thu Jun 20 16:35:45 2002
@@ -19,6 +19,9 @@
mainmenu_option next_comment
comment 'Processor type and features'
bool 'Symmetric multi-processing support' CONFIG_SMP
+if [ "$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 [ "$CONFIG_S390_SUPPORT" = "y" ]; then
tristate 'Kernel support for 31 bit ELF binaries' CONFIG_BINFMT_ELF32
diff -urN linux-2.5.24/arch/s390x/defconfig linux/arch/s390x/defconfig
--- linux-2.5.24/arch/s390x/defconfig Thu Jun 20 15:53:41 2002
+++ linux/arch/s390x/defconfig Thu Jun 20 16:35:45 2002
@@ -36,6 +36,7 @@
CONFIG_SMP=y
CONFIG_S390_SUPPORT=y
CONFIG_BINFMT_ELF32=y
+CONFIG_NR_CPUS=64
#
# Base setup
diff -urN linux-2.5.24/arch/sparc/config.in linux/arch/sparc/config.in
--- linux-2.5.24/arch/sparc/config.in Thu Jun 20 15:53:44 2002
+++ linux/arch/sparc/config.in Thu Jun 20 16:35:45 2002
@@ -17,6 +17,10 @@
bool 'Symmetric multi-processing support (does not work on sun4/sun4c)' CONFIG_SMP
+if [ "$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-2.5.24/arch/sparc64/config.in linux/arch/sparc64/config.in
--- linux-2.5.24/arch/sparc64/config.in Thu Jun 20 15:53:49 2002
+++ linux/arch/sparc64/config.in Thu Jun 20 16:35:45 2002
@@ -17,6 +17,10 @@
bool 'Symmetric multi-processing support' CONFIG_SMP
bool 'Preemptible Kernel' CONFIG_PREEMPT
+if [ "$CONFIG_SMP" = "y" ]; then
+ int 'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
+fi
+
# Identify this as a Sparc64 build
define_bool CONFIG_SPARC64 y
diff -urN linux-2.5.24/arch/sparc64/defconfig linux/arch/sparc64/defconfig
--- linux-2.5.24/arch/sparc64/defconfig Thu Jun 20 15:53:49 2002
+++ linux/arch/sparc64/defconfig Thu Jun 20 16:35:45 2002
@@ -63,6 +63,7 @@
CONFIG_BINFMT_MISC=m
# CONFIG_SUNOS_EMUL is not set
CONFIG_SOLARIS_EMUL=m
+CONFIG_NR_CPUS=64
#
# Parallel port support
diff -urN linux-2.5.24/arch/x86_64/config.in linux/arch/x86_64/config.in
--- linux-2.5.24/arch/x86_64/config.in Thu Jun 20 15:53:47 2002
+++ linux/arch/x86_64/config.in Thu Jun 20 16:35:45 2002
@@ -54,6 +54,7 @@
fi
if [ "$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-2.5.24/arch/x86_64/defconfig linux/arch/x86_64/defconfig
--- linux-2.5.24/arch/x86_64/defconfig Thu Jun 20 15:53:55 2002
+++ linux/arch/x86_64/defconfig Thu Jun 20 16:35:45 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-2.5.24/include/linux/threads.h linux/include/linux/threads.h
--- linux-2.5.24/include/linux/threads.h Thu Jun 20 15:53:42 2002
+++ linux/include/linux/threads.h Thu Jun 20 16:35:45 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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