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Configurable NR_CPUS for 2.5.24

PATCH New Robert Love 1 participant 1 message Jun 24, 2002

Subsystems (5)
MIPS s390 SPARC + UltraSPARC (sparc/sparc64) PA-RISC architecture +1 more subsystems
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Robert Love

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PATCH 1/1 Configurable NR_CPUS for 2.5.24

This is in 2.5-dj now and thus I have gotten a couple emails for a resync against 2.5 proper... so here we go, live from the Kernel Summit.

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

arch/alpha/config.in +1 -0
diff -urN linux-2.5.24/arch/alpha/config.in linux/arch/alpha/config.in
@@ -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
arch/i386/Config.help +8 -0
diff -urN linux-2.5.24/arch/i386/Config.help linux/arch/i386/Config.help
@@ -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
arch/i386/config.in +1 -0
diff -urN linux-2.5.24/arch/i386/config.in linux/arch/i386/config.in
@@ -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
arch/i386/defconfig +1 -0
diff -urN linux-2.5.24/arch/i386/defconfig linux/arch/i386/defconfig
@@ -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
arch/ia64/config.in +4 -0
diff -urN linux-2.5.24/arch/ia64/config.in linux/arch/ia64/config.in
@@ -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
arch/ia64/defconfig +1 -0
diff -urN linux-2.5.24/arch/ia64/defconfig linux/arch/ia64/defconfig
@@ -61,6 +61,7 @@
 CONFIG_EFI_VARS=y
 CONFIG_BINFMT_ELF=y
 # CONFIG_BINFMT_MISC is not set
+CONFIG_NR_CPUS=64
 
 #
 # ACPI Support
arch/mips/config.in +2 -0
diff -urN linux-2.5.24/arch/mips/config.in linux/arch/mips/config.in
@@ -500,6 +500,8 @@
 bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
 if [ "$CONFIG_SMP" != "y" ]; then
    bool 'Run uncached' CONFIG_MIPS_UNCACHED
+else
+   int  'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
 fi
 endmenu
arch/mips64/config.in +2 -0
diff -urN linux-2.5.24/arch/mips64/config.in linux/arch/mips64/config.in
@@ -245,6 +245,8 @@
 bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
 if [ "$CONFIG_SMP" != "y" ]; then
    bool 'Run uncached' CONFIG_MIPS_UNCACHED
+else
+   int  'Maximum number of CPUs (2-64)' CONFIG_NR_CPUS 64
 fi
 endmenu
arch/mips64/defconfig +1 -0
diff -urN linux-2.5.24/arch/mips64/defconfig linux/arch/mips64/defconfig
@@ -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
arch/parisc/config.in +4 -0
diff -urN linux-2.5.24/arch/parisc/config.in linux/arch/parisc/config.in
@@ -18,6 +18,10 @@
 # bool 'Symmetric multi-processing support' CONFIG_SMP
 define_bool CONFIG_SMP n
 
+if [ "$CONFIG_SMP" = "y" ]; then
+   int  'Maximum number of CPUs (2-32)' CONFIG_NR_CPUS 32
+fi
+
 bool 'Kernel Debugger support' CONFIG_KWDB
 # define_bool CONFIG_KWDB n
arch/ppc/config.in +1 -0
diff -urN linux-2.5.24/arch/ppc/config.in linux/arch/ppc/config.in
@@ -172,6 +172,7 @@
 bool 'Symmetric multi-processing support' CONFIG_SMP
 if [ "$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 [ "$CONFIG_SMP" != "y" ]; then
    bool 'Preemptible Kernel' CONFIG_PREEMPT
arch/ppc64/config.in +1 -0
diff -urN linux-2.5.24/arch/ppc64/config.in linux/arch/ppc64/config.in
@@ -21,6 +21,7 @@
 bool 'Symmetric multi-processing support' CONFIG_SMP
 if [ "$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
arch/ppc64/defconfig +1 -0
diff -urN linux-2.5.24/arch/ppc64/defconfig linux/arch/ppc64/defconfig
@@ -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
arch/s390/config.in +3 -0
diff -urN linux-2.5.24/arch/s390/config.in linux/arch/s390/config.in
@@ -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
arch/s390/defconfig +1 -0
diff -urN linux-2.5.24/arch/s390/defconfig linux/arch/s390/defconfig
@@ -35,6 +35,7 @@
 #
 CONFIG_SMP=y
 CONFIG_MATHEMU=y
+CONFIG_NR_CPUS=64
 
 #
 # Base setup
arch/s390x/config.in +3 -0
diff -urN linux-2.5.24/arch/s390x/config.in linux/arch/s390x/config.in
@@ -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
arch/s390x/defconfig +1 -0
diff -urN linux-2.5.24/arch/s390x/defconfig linux/arch/s390x/defconfig
@@ -36,6 +36,7 @@
 CONFIG_SMP=y
 CONFIG_S390_SUPPORT=y
 CONFIG_BINFMT_ELF32=y
+CONFIG_NR_CPUS=64
 
 #
 # Base setup
arch/sparc/config.in +4 -0
diff -urN linux-2.5.24/arch/sparc/config.in linux/arch/sparc/config.in
@@ -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
arch/sparc64/config.in +4 -0
diff -urN linux-2.5.24/arch/sparc64/config.in linux/arch/sparc64/config.in
@@ -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
arch/sparc64/defconfig +1 -0
diff -urN linux-2.5.24/arch/sparc64/defconfig linux/arch/sparc64/defconfig
@@ -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
arch/x86_64/config.in +1 -0
diff -urN linux-2.5.24/arch/x86_64/config.in linux/arch/x86_64/config.in
@@ -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
arch/x86_64/defconfig +1 -0
diff -urN linux-2.5.24/arch/x86_64/defconfig linux/arch/x86_64/defconfig
@@ -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
include/linux/threads.h +8 -2
diff -urN linux-2.5.24/include/linux/threads.h linux/include/linux/threads.h
@@ -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