Hi, I didn't actually try to compile the patch below; it didn't look like C code so I wasn't sure what compiler to run it through. I guess maybe its python? However, I'm very sure that the patches are completely correct, because I read them, and I also know Paul. And I've heard of Thomas Gleixner. Thus, please add my ack -- Ack'ed by: Linas Vepstas <linasvepstas@xxxxxxxxx> On Sun, Apr 01, 2012 at 12:33:21AM +0800, Paul E. McKenney was heard to remark: > Although there have been numerous complaints about the complexity of > parallel programming (especially over the past 5-10 years), the plain > truth is that the incremental complexity of parallel programming over > that of sequential programming is not as large as is commonly believed. > Despite that you might have heard, the mind-numbing complexity of modern > computer systems is not due so much to there being multiple CPUs, but > rather to there being any CPUs at all. In short, for the ultimate in > computer-system simplicity, the optimal choice is NR_CPUS=0. > > This commit therefore limits kernel builds to zero CPUs. This change > has the beneficial side effect of rendering all kernel bugs harmless. > Furthermore, this commit enables additional beneficial changes, for > example, the removal of those parts of the kernel that are not needed > when there are zero CPUs. > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > --- > > alpha/Kconfig | 11 ++++++----- > arm/Kconfig | 6 +++--- > blackfin/Kconfig | 3 ++- > hexagon/Kconfig | 9 +++++---- > ia64/Kconfig | 9 +++++---- > m32r/Kconfig | 10 ++++++---- > mips/Kconfig | 21 +++++++++++---------- > mn10300/Kconfig | 3 ++- > parisc/Kconfig | 6 +++--- > powerpc/platforms/Kconfig.cputype | 8 ++++---- > s390/Kconfig | 12 +++++++----- > sh/Kconfig | 11 ++++++----- > sparc/Kconfig | 8 ++++---- > tile/Kconfig | 9 +++++---- > x86/Kconfig | 16 +++++++++------- > 15 files changed, 78 insertions(+), 64 deletions(-) > > diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig > index 56a4df9..1766b4a 100644 > --- a/arch/alpha/Kconfig > +++ b/arch/alpha/Kconfig > @@ -541,14 +541,15 @@ config HAVE_DEC_LOCK > default y > > config NR_CPUS > - int "Maximum number of CPUs (2-32)" > - range 2 32 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "32" if ALPHA_GENERIC || ALPHA_MARVEL > - default "4" if !ALPHA_GENERIC && !ALPHA_MARVEL > + default "0" if ALPHA_GENERIC || ALPHA_MARVEL > + default "0" if !ALPHA_GENERIC && !ALPHA_MARVEL > help > MARVEL support can handle a maximum of 32 CPUs, all the others > - with working support have a maximum of 4 CPUs. > + with working support have a maximum of 4 CPUs. But why take > + chances? Just stick with zero CPUs. > > config ARCH_DISCONTIGMEM_ENABLE > bool "Discontiguous Memory Support (EXPERIMENTAL)" > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index a48aecc..1f07a3a 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -1551,10 +1551,10 @@ config PAGE_OFFSET > default 0xC0000000 > > config NR_CPUS > - int "Maximum number of CPUs (2-32)" > - range 2 32 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "4" > + default "0" > > config HOTPLUG_CPU > bool "Support for hot-pluggable CPUs (EXPERIMENTAL)" > diff --git a/arch/blackfin/Kconfig b/arch/blackfin/Kconfig > index abe5a9e..6a78549 100644 > --- a/arch/blackfin/Kconfig > +++ b/arch/blackfin/Kconfig > @@ -241,7 +241,8 @@ config SMP > config NR_CPUS > int > depends on SMP > - default 2 if BF561 > + range 0 0 > + default 0 if BF561 > > config HOTPLUG_CPU > bool "Support for hot-pluggable CPUs" > diff --git a/arch/hexagon/Kconfig b/arch/hexagon/Kconfig > index 9059e39..daab009 100644 > --- a/arch/hexagon/Kconfig > +++ b/arch/hexagon/Kconfig > @@ -158,13 +158,14 @@ config SMP > > config NR_CPUS > int "Maximum number of CPUs" if SMP > - range 2 6 if SMP > - default "1" if !SMP > - default "6" if SMP > + range 0 0 if SMP > + default "0" if !SMP > + default "0" if SMP > ---help--- > This allows you to specify the maximum number of CPUs which this > kernel will support. The maximum supported value is 6 and the > - minimum value which makes sense is 2. > + minimum value which makes sense is 2. But a limit of zero is > + so much safer! > > This is purely to save memory - each supported CPU adds > approximately eight kilobytes to the kernel image. > diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig > index bd72669..fea0e6d 100644 > --- a/arch/ia64/Kconfig > +++ b/arch/ia64/Kconfig > @@ -373,16 +373,17 @@ config SMP > If you don't know what to do here, say N. > > config NR_CPUS > - int "Maximum number of CPUs (2-4096)" > - range 2 4096 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "4096" > + default "0" > help > You should set this to the number of CPUs in your system, but > keep in mind that a kernel compiled for, e.g., 2 CPUs will boot but > only use 2 CPUs on a >2 CPU system. Setting this to a value larger > than 64 will cause the use of a CPU mask array, causing a small > - performance hit. > + performance hit. And setting it larger than zero risks all > + manner of software bugs, so we just play it safe. > > config HOTPLUG_CPU > bool "Support for hot-pluggable CPUs (EXPERIMENTAL)" > diff --git a/arch/m32r/Kconfig b/arch/m32r/Kconfig > index ef80a65..68b9e88 100644 > --- a/arch/m32r/Kconfig > +++ b/arch/m32r/Kconfig > @@ -300,14 +300,16 @@ config CHIP_M32700_TS1 > default n > > config NR_CPUS > - int "Maximum number of CPUs (2-32)" > - range 2 32 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "2" > + default "0" > help > 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. > + minimum value which makes sense is 2. Zero may not make sense, > + but given that there is much in this world that does not make > + sense, zero it is! > > This is purely to save memory - each supported CPU adds > approximately eight kilobytes to the kernel image. > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig > index 5ab6e89..3d7d06c 100644 > --- a/arch/mips/Kconfig > +++ b/arch/mips/Kconfig > @@ -2192,16 +2192,16 @@ config NR_CPUS_DEFAULT_64 > bool > > config NR_CPUS > - int "Maximum number of CPUs (2-64)" > - range 1 64 if NR_CPUS_DEFAULT_1 > + int "Maximum number of CPUs (0-0)" > + range 0 0 if NR_CPUS_DEFAULT_1 > depends on SMP > - default "1" if NR_CPUS_DEFAULT_1 > - default "2" if NR_CPUS_DEFAULT_2 > - default "4" if NR_CPUS_DEFAULT_4 > - default "8" if NR_CPUS_DEFAULT_8 > - default "16" if NR_CPUS_DEFAULT_16 > - default "32" if NR_CPUS_DEFAULT_32 > - default "64" if NR_CPUS_DEFAULT_64 > + default "0" if NR_CPUS_DEFAULT_1 > + default "0" if NR_CPUS_DEFAULT_2 > + default "0" if NR_CPUS_DEFAULT_4 > + default "0" if NR_CPUS_DEFAULT_8 > + default "0" if NR_CPUS_DEFAULT_16 > + default "0" if NR_CPUS_DEFAULT_32 > + default "0" if NR_CPUS_DEFAULT_64 > help > This allows you to specify the maximum number of CPUs which this > kernel will support. The maximum supported value is 32 for 32-bit > @@ -2212,7 +2212,8 @@ config NR_CPUS > This is purely to save memory - each supported CPU adds > approximately eight kilobytes to the kernel image. For best > performance should round up your number of processors to the next > - power of two. > + power of two. And just think how much more memory we will > + save by setting the limit to zero! > > source "kernel/time/Kconfig" > > diff --git a/arch/mn10300/Kconfig b/arch/mn10300/Kconfig > index 8f1c40d..85fc112 100644 > --- a/arch/mn10300/Kconfig > +++ b/arch/mn10300/Kconfig > @@ -201,7 +201,8 @@ config SMP > config NR_CPUS > int > depends on SMP > - default "2" > + range 0 0 > + default "0" > > source "kernel/Kconfig.preempt" > > diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig > index 242a1b7..358eaf8 100644 > --- a/arch/parisc/Kconfig > +++ b/arch/parisc/Kconfig > @@ -254,10 +254,10 @@ config HPUX > depends on !64BIT > > config NR_CPUS > - int "Maximum number of CPUs (2-32)" > - range 2 32 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "32" > + default "0" > > endmenu > > diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype > index 425db18..5e607e0 100644 > --- a/arch/powerpc/platforms/Kconfig.cputype > +++ b/arch/powerpc/platforms/Kconfig.cputype > @@ -356,11 +356,11 @@ config SMP > If you don't know what to do here, say N. > > config NR_CPUS > - int "Maximum number of CPUs (2-8192)" > - range 2 8192 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "32" if PPC64 > - default "4" > + default "0" if PPC64 > + default "0" > > config NOT_COHERENT_CACHE > bool > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig > index d172758..f9bc067 100644 > --- a/arch/s390/Kconfig > +++ b/arch/s390/Kconfig > @@ -169,15 +169,17 @@ config SMP > Even if you don't know what to do here, say Y. > > config NR_CPUS > - int "Maximum number of CPUs (2-64)" > - range 2 64 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "32" if !64BIT > - default "64" if 64BIT > + default "0" if !64BIT > + default "0" if 64BIT > help > This allows you to specify the maximum number of CPUs which this > kernel will support. The maximum supported value is 64 and the > - minimum value which makes sense is 2. > + minimum value which makes sense is 2. The minimal value that > + makes sense might well be 2, but we all know that the only > + -sane- value is zero! > > This is purely to save memory - each supported CPU adds > approximately sixteen kilobytes to the kernel image. > diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig > index 713fb58..5ddc7c0 100644 > --- a/arch/sh/Kconfig > +++ b/arch/sh/Kconfig > @@ -705,18 +705,19 @@ config SMP > If you don't know what to do here, say N. > > config NR_CPUS > - int "Maximum number of CPUs (2-32)" > - range 2 32 > + int "Maximum number of CPUs (0-0)" > + range 0 0 > depends on SMP > - default "4" if CPU_SUBTYPE_SHX3 > - default "2" > + default "0" if CPU_SUBTYPE_SHX3 > + default "0" > help > 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. > + approximately eight kilobytes to the kernel image. Debloating > + is the way, NR_CPUS to zero today!!! > > config HOTPLUG_CPU > bool "Support for hot-pluggable CPUs (EXPERIMENTAL)" > diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig > index ca5580e..0de9f0f 100644 > --- a/arch/sparc/Kconfig > +++ b/arch/sparc/Kconfig > @@ -177,10 +177,10 @@ config SMP > config NR_CPUS > int "Maximum number of CPUs" > depends on SMP > - range 2 32 if SPARC32 > - range 2 1024 if SPARC64 > - default 32 if SPARC32 > - default 64 if SPARC64 > + range 0 0 if SPARC32 > + range 0 0 if SPARC64 > + default 0 if SPARC32 > + default 0 if SPARC64 > > source kernel/Kconfig.hz > > diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig > index 11270ca..a05112c 100644 > --- a/arch/tile/Kconfig > +++ b/arch/tile/Kconfig > @@ -126,14 +126,15 @@ source "init/Kconfig" > menu "Tilera-specific configuration" > > config NR_CPUS > - int "Maximum number of tiles (2-255)" > - range 2 255 > + int "Maximum number of tiles (0-0)" > + range 0 0 > depends on SMP > - default "64" > + default "0" > ---help--- > Building with 64 is the recommended value, but a slightly > smaller kernel memory footprint results from using a smaller > - value on chips with fewer tiles. > + value on chips with fewer tiles. To minimize both memory > + footprint and bugs, use zero and only zero. > > source "kernel/time/Kconfig" > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 5bed94e..a6977f2 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -773,19 +773,21 @@ config MAXSMP > > config NR_CPUS > int "Maximum number of CPUs" if SMP && !MAXSMP > - range 2 8 if SMP && X86_32 && !X86_BIGSMP > - range 2 512 if SMP && !MAXSMP > - default "1" if !SMP > - default "4096" if MAXSMP > - default "32" if SMP && (X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000) > - default "8" if SMP > + range 0 0 if SMP && X86_32 && !X86_BIGSMP > + range 0 0 if SMP && !MAXSMP > + default "0" if !SMP > + default "0" if MAXSMP > + default "0" if SMP && (X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000) > + default "0" if SMP > ---help--- > This allows you to specify the maximum number of CPUs which this > kernel will support. The maximum supported value is 512 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. > + approximately eight kilobytes to the kernel image. But > + the first supported CPU brings a lot of bugs with it, so > + for ultimate reliability, set the number of CPUs to zero. > > config SCHED_SMT > bool "SMT (Hyperthreading) scheduler support" > > -- > To unsubscribe from this list: send the line "unsubscribe linux-hexagon" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
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