lkml.org 
[lkml]   [2012]   [Mar]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH RFC] Simplify the Linux kernel by reducing its state space
    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@linux.vnet.ibm.com>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.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"


    \
     
     \ /
      Last update: 2012-03-31 18:35    [W:0.041 / U:60.324 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site