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Message-ID: <20120331201422.GG2450@linux.vnet.ibm.com> Date: Sat, 31 Mar 2012 13:14:22 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Linas Vepstas <linasvepstas@...il.com> Cc: linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, uclinux-dist-devel@...ckfin.uclinux.org, linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org, linux-m32r@...linux-m32r.org, linux-m32r-ja@...linux-m32r.org, linux-mips@...ux-mips.org, linux-am33-list@...hat.com, linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org, linux-sh@...r.kernel.org, sparclinux@...r.kernel.org, tglx@...utronix.de, linux@....linux.org.uk, dhowells@...hat.com, jejb@...isc-linux.org, linux390@...ibm.com, x86@...nel.org, cmetcalf@...era.com Subject: Re: [PATCH RFC] Simplify the Linux kernel by reducing its state space On Sat, Mar 31, 2012 at 02:57:46PM -0500, Linas Vepstas wrote: > 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 that Paul is a trustworthy programmer. > Thus, please add my ack > > Ack'ed by: Linas Vepstas <linasvepstas@...il.com> It is Linux-kernel Kconfig language, which processed during kernel builds. I have added your Acked-by. ;-) Thanx, Paul > On 31 March 2012 11:33, Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote: > > > 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@...ux.vnet.ibm.com> > > Reviewed-by: Thomas Gleixner <tglx@...utronix.de> > > --- > > > > 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@...r.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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