How to configure the Linux kernel/Processor type and features

Processor type and features

"Subarchitecture Type"

• • default X86_PC

• Option: X86_PC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) PC-compatible

    Choose this option if your computer is a standard PC or compatible.

• Option: X86_ELAN
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) AMD Elan

    Select this for an AMD Elan processor.

    Do not use this option for K6/Athlon/Opteron processors!

    If unsure, choose "PC-compatible" instead.

• Option: X86_VOYAGER
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Voyager (NCR)

    Voyager is an MCA-based 32-way capable SMP architecture proprietary to NCR Corp. Machine classes 345x/35xx/4100/51xx are Voyager-based.

    *** WARNING ***

    If you do not specifically know you have a Voyager based machine, say N here, otherwise the kernel you build will not be bootable.

• Option: X86_NUMAQ
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) NUMAQ (IBM/Sequent)
  • select NUMA

    This option is used for getting Linux to run on a (IBM/Sequent) NUMA multiquad box. This changes the way that processors are bootstrapped, and uses Clustered Logical APIC addressing mode instead of Flat Logical. You will need a new lynxer.elf file to flash your firmware with - send email to <Martin.Bligh@us.ibm.com>.

• Option: X86_SUMMIT
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Summit/EXA (IBM x440)
  • depends on SMP

    This option is needed for IBM systems that use the Summit/EXA chipset. In particular, it is needed for the x440.

    If you don't have one of these computers, you should say N here.

• Option: X86_BIGSMP
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Support for other sub-arch SMP systems with more than 8 CPUs
  • depends on SMP

    This option is needed for the systems that have more than 8 CPUs and if the system is not of any sub-arch type above.

    If you don't have such a system, you should say N here.

• Option: X86_VISWS
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) SGI 320/540 (Visual Workstation)

    The SGI Visual Workstation series is an IA32-based workstation based on SGI systems chips with some legacy PC hardware attached.

    Say Y here to create a kernel to run on the SGI 320 or 540.

    A kernel compiled for the Visual Workstation will not run on PCs and vice versa. See <file:Documentation/sgi-visws.txt> for details.

• Option: X86_GENERICARCH
  • Kernel Versions: 2.6.15.6 ... bool Generic architecture (Summit, bigsmp, ES7000, default) depends on SMP help This option compiles in the Summit, bigsmp, ES7000, default subarchitectures. It is intended for a generic binary kernel.

• Option: X86_ES7000
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Support for Unisys ES7000 IA32 series
  • depends on SMP

    Support for Unisys ES7000 systems. Say 'Y' here if this kernel is supposed to run on an IA32-based Unisys ES7000 system. Only choose this option if you have such a system, otherwise you should say N here.

• Option: ACPI_SRAT
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • default y
  • depends on NUMA && (X86_SUMMIT || X86_GENERICARCH)

• Option: X86_SUMMIT_NUMA
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • default y
  • depends on NUMA && (X86_SUMMIT || X86_GENERICARCH)

• Option: X86_CYCLONE_TIMER
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • default y
  • depends on X86_SUMMIT || X86_GENERICARCH

• Option: ES7000_CLUSTERED_APIC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • default y
  • depends on SMP && X86_ES7000 && MPENTIUMIII

• Option: Howto configure the Linux kernel/arch/i386.cpu"

• Option: HPET_TIMER
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) HPET Timer Support

    This enables the use of the HPET for the kernel's internal timer. HPET is the next generation timer replacing legacy 8254s. You can safely choose Y here. However, HPET will only be activated if the platform and the BIOS support this feature. Otherwise the 8254 will be used for timing services.

    Choose N to continue using the legacy 8254 timer.

• Option: HPET_EMULATE_RTC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on HPET_TIMER && RTC=y
  • default y

• Option: SMP
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Symmetric multi-processing support

    This enables support for systems with more than one CPU. If you have a system with only one CPU, like most personal computers, say N. If you have a system with more than one CPU, say Y.

    If you say N here, the kernel will run on single and multiprocessor machines, but will use only one CPU of a multiprocessor machine. If you say Y here, the kernel will run on many, but not all, singleprocessor machines. On a singleprocessor machine, the kernel will run faster if you say N here.

    Note that if you say Y here and choose architecture "586" or Pentium under Processor family, the kernel will not work on 486 architectures. Similarly, multiprocessor kernels for the "PPro" architecture may not work on all Pentium based boards.

    People using multiprocessor machines who say Y here should also say Y to "Enhanced Real Time Clock Support", below. The "Advanced Power Management" code will be disabled if you say Y here.

    See also the <file:Documentation/smp.txt>, <file:Documentation/i386/IO-APIC.txt>, <file:Documentation/nmi_watchdog.txt> and the SMP-HOWTO available at <http://www.tldp.org/docs.html#howto>.

    If you don't know what to do here, say N.

• Option: NR_CPUS
  • Kernel Versions: 2.6.15.6 ...

"Maximum number of CPUs (2-255)" 2 255

• • depends on SMP
  • default "32" if X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000
  • default "8"

    This allows you to specify the maximum number of CPUs which this kernel will support. The maximum supported value is 255 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.

• Option: SCHED_SMT
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) SMT (Hyperthreading) scheduler support
  • depends on SMP
  • default off

    SMT scheduler support improves the CPU scheduler's decision making when dealing with Intel Pentium 4 chips with HyperThreading at a cost of slightly increased overhead in some places. If unsure say N here.

• Option: Howto configure the Linux kernel/kernel.preempt"

• Option: X86_UP_APIC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Local APIC support on uniprocessors
  • depends on !SMP && !(X86_VISWS || X86_VOYAGER)

    A local APIC (Advanced Programmable Interrupt Controller) is an integrated interrupt controller in the CPU. If you have a single-CPU system which has a processor with a local APIC, you can say Y here to enable and use it. If you say Y here even though your machine doesn't have a local APIC, then the kernel will still run with no slowdown at all. The local APIC supports CPU-generated self-interrupts (timer, performance counters), and the NMI watchdog which detects hard lockups.

• Option: X86_UP_IOAPIC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) IO-APIC support on uniprocessors
  • depends on X86_UP_APIC

    An IO-APIC (I/O Advanced Programmable Interrupt Controller) is an SMP-capable replacement for PC-style interrupt controllers. Most SMP systems and many recent uniprocessor systems have one.

    If you have a single-CPU system with an IO-APIC, you can say Y here to use it. If you say Y here even though your machine doesn't have an IO-APIC, then the kernel will still run with no slowdown at all.

• Option: X86_LOCAL_APIC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on X86_UP_APIC || ((X86_VISWS || SMP) && !X86_VOYAGER)
  • default y

• Option: X86_IO_APIC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on X86_UP_IOAPIC || (SMP && !(X86_VISWS || X86_VOYAGER))
  • default y

• Option: X86_VISWS_APIC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on X86_VISWS
  • default y

• Option: X86_MCE
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Machine Check Exception
  • depends on !X86_VOYAGER

    Machine Check Exception support allows the processor to notify the kernel if it detects a problem (e.g. overheating, component failure). The action the kernel takes depends on the severity of the problem, ranging from a warning message on the console, to halting the machine. Your processor must be a Pentium or newer to support this - check the flags in /proc/cpuinfo for mce. Note that some older Pentium systems have a design flaw which leads to false MCE events - hence MCE is disabled on all P5 processors, unless explicitly enabled with "mce" as a boot argument. Similarly, if MCE is built in and creates a problem on some new non-standard machine, you can boot with "nomce" to disable it. MCE support simply ignores non-MCE processors like the 386 and 486, so nearly everyone can say Y here.

• Option: X86_MCE_NONFATAL
  • Kernel Versions: 2.6.15.6 ...
  • (on/off/module) Check for non-fatal errors on AMD Athlon/Duron / Intel Pentium 4
  • depends on X86_MCE

    Enabling this feature starts a timer that triggers every 5 seconds which will look at the machine check registers to see if anything happened. Non-fatal problems automatically get corrected (but still logged). Disable this if you don't want to see these messages. Seeing the messages this option prints out may be indicative of dying hardware, or out-of-spec (i.e., overclocked) hardware. This option only does something on certain CPUs. (AMD Athlon/Duron and Intel Pentium 4)

• Option: X86_MCE_P4THERMAL
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) check for P4 thermal throttling interrupt.
  • depends on X86_MCE && (X86_UP_APIC || SMP) && !X86_VISWS

    Enabling this feature will cause a message to be printed when the P4 enters thermal throttling.

• Option: TOSHIBA
  • Kernel Versions: 2.6.15.6 ...
  • (on/off/module) Toshiba Laptop support

    This adds a driver to safely access the System Management Mode of the CPU on Toshiba portables with a genuine Toshiba BIOS. It does not work on models with a Phoenix BIOS. The System Management Mode is used to set the BIOS and power saving options on Toshiba portables.

    For information on utilities to make use of this driver see the Toshiba Linux utilities web site at: <http://www.buzzard.org.uk/toshiba/>.

    Say Y if you intend to run this kernel on a Toshiba portable. Say N otherwise.

• Option: I8K
  • Kernel Versions: 2.6.15.6 ...
  • (on/off/module) Dell laptop support

    This adds a driver to safely access the System Management Mode of the CPU on the Dell Inspiron 8000. The System Management Mode is used to read cpu temperature and cooling fan status and to control the fans on the I8K portables.

    This driver has been tested only on the Inspiron 8000 but it may also work with other Dell laptops. You can force loading on other models by passing the parameter `force=1' to the module. Use at your own risk.

    For information on utilities to make use of this driver see the I8K Linux utilities web site at: <http://people.debian.org/~dz/i8k/>

    Say Y if you intend to run this kernel on a Dell Inspiron 8000. Say N otherwise.

• Option: X86_REBOOTFIXUPS
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Enable X86 board specific fixups for reboot
  • depends on X86
  • default n

    This enables chipset and/or board specific fixups to be done in order to get reboot to work correctly. This is only needed on some combinations of hardware and BIOS. The symptom, for which this config is intended, is when reboot ends with a stalled/hung system.

    Currently, the only fixup is for the Geode GX1/CS5530A/TROM2.1. combination.

    Say Y if you want to enable the fixup. Currently, it's safe to enable this option even if you don't need it. Say N otherwise.

• Option: MICROCODE
  • Kernel Versions: 2.6.15.6 ...
  • (on/off/module) /dev/cpu/microcode - Intel IA32 CPU microcode support

    If you say Y here and also to "/dev file system support" in the 'File systems' section, you will be able to update the microcode on Intel processors in the IA32 family, e.g. Pentium Pro, Pentium II, Pentium III, Pentium 4, Xeon etc. You will obviously need the actual microcode binary data itself which is not shipped with the Linux kernel.

    For latest news and information on obtaining all the required ingredients for this driver, check: <http://www.urbanmyth.org/microcode/>.

    To compile this driver as a module, choose M here: the module will be called microcode.

• Option: X86_MSR
  • Kernel Versions: 2.6.15.6 ...
  • (on/off/module) /dev/cpu/*/msr - Model-specific register support

    This device gives privileged processes access to the x86 Model-Specific Registers (MSRs). It is a character device with major 202 and minors 0 to 31 for /dev/cpu/0/msr to /dev/cpu/31/msr. MSR accesses are directed to a specific CPU on multi-processor systems.

• Option: X86_CPUID
  • Kernel Versions: 2.6.15.6 ...
  • (on/off/module) /dev/cpu/*/cpuid - CPU information support

    This device gives processes access to the x86 CPUID instruction to be executed on a specific processor. It is a character device with major 203 and minors 0 to 31 for /dev/cpu/0/cpuid to /dev/cpu/31/cpuid.

• Option: Howto configure the Linux kernel/drivers/firmware

"High Memory Support"

• • default NOHIGHMEM

• Option: NOHIGHMEM
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) off

    Linux can use up to 64 Gigabytes of physical memory on x86 systems. However, the address space of 32-bit x86 processors is only 4 Gigabytes large. That means that, if you have a large amount of physical memory, not all of it can be "permanently mapped" by the kernel. The physical memory that's not permanently mapped is called high memory.

    If you are compiling a kernel which will never run on a machine with more than 1 Gigabyte total physical RAM, answer "off" here (default choice and suitable for most users). This will result in a "3GB/1GB" split: 3GB are mapped so that each process sees a 3GB virtual memory space and the remaining part of the 4GB virtual memory space is used by the kernel to permanently map as much physical memory as possible.

    If the machine has between 1 and 4 Gigabytes physical RAM, then answer "4GB" here.

    If more than 4 Gigabytes is used then answer "64GB" here. This selection turns Intel PAE (Physical Address Extension) mode on. PAE implements 3-level paging on IA32 processors. PAE is fully supported by Linux, PAE mode is implemented on all recent Intel processors (Pentium Pro and better). NOTE: If you say "64GB" here, then the kernel will not boot on CPUs that don't support PAE!

    The actual amount of total physical memory will either be auto detected or can be forced by using a kernel command line option such as "mem=256M". (Try "man bootparam" or see the documentation of your boot loader (lilo or loadlin) about how to pass options to the kernel at boot time.)

    If unsure, say "off".

• Option: HIGHMEM4G
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) 4GB

    Select this if you have a 32-bit processor and between 1 and 4 gigabytes of physical RAM.

• Option: HIGHMEM64G
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) 64GB

    Select this if you have a 32-bit processor and more than 4 gigabytes of physical RAM.

• Option: HIGHMEM
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on HIGHMEM64G || HIGHMEM4G
  • default y

• Option: X86_PAE
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on HIGHMEM64G
  • default y

Common NUMA Features

• Option: NUMA
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Numa Memory Allocation and Scheduler Support
  • depends on SMP && HIGHMEM64G && (X86_NUMAQ || X86_GENERICARCH || (X86_SUMMIT && ACPI))
  • default n if X86_PC
  • default y if (X86_NUMAQ || X86_SUMMIT)
  • select SPARSEMEM_STATIC

Need comments to help the hapless user trying to turn on NUMA support

"NUMA (NUMA-Q) requires SMP, 64GB highmem support"

• • depends on X86_NUMAQ && (!HIGHMEM64G || !SMP)

"NUMA (Summit) requires SMP, 64GB highmem support, ACPI"

• • depends on X86_SUMMIT && (!HIGHMEM64G || !ACPI)

• Option: HAVE_ARCH_BOOTMEM_NODE
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on NUMA
  • default y

• Option: ARCH_HAVE_MEMORY_PRESENT
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on DISCONTIGMEM
  • default y

• Option: NEED_NODE_MEMMAP_SIZE
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on DISCONTIGMEM || SPARSEMEM
  • default y

• Option: HAVE_ARCH_ALLOC_REMAP
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on NUMA
  • default y

• Option: ARCH_DISCONTIGMEM_ENABLE
  • Kernel Versions: 2.6.15.6 ...

_bool y

• • depends on NUMA

• Option: ARCH_DISCONTIGMEM_DEFAULT
  • Kernel Versions: 2.6.15.6 ...

_bool y

• • depends on NUMA

• Option: ARCH_SPARSEMEM_ENABLE
  • Kernel Versions: 2.6.15.6 ...

_bool y

• • depends on NUMA

• Option: ARCH_SELECT_MEMORY_MODEL
  • Kernel Versions: 2.6.15.6 ...

_bool y

• • depends on ARCH_SPARSEMEM_ENABLE

• Option: Howto configure the Linux kernel/mm

• Option: HAVE_ARCH_EARLY_PFN_TO_NID
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • default y
  • depends on NUMA

• Option: HIGHPTE
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Allocate 3rd-level pagetables from highmem
  • depends on HIGHMEM4G || HIGHMEM64G

    The VM uses one page table entry for each page of physical memory. For systems with a lot of RAM, this can be wasteful of precious low memory. Setting this option will put user-space page table entries in high memory.

• Option: MATH_EMULATION
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Math emulation

    Linux can emulate a math coprocessor (used for floating point operations) if you don't have one. 486DX and Pentium processors have a math coprocessor built in, 486SX and 386 do not, unless you added a 487DX or 387, respectively. (The messages during boot time can give you some hints here ["man dmesg"].) Everyone needs either a coprocessor or this emulation.

    If you don't have a math coprocessor, you need to say Y here; if you say Y here even though you have a coprocessor, the coprocessor will be used nevertheless. (This behavior can be changed with the kernel command line option "no387", which comes handy if your coprocessor is broken. Try "man bootparam" or see the documentation of your boot loader (lilo or loadlin) about how to pass options to the kernel at boot time.) This means that it is a good idea to say Y here if you intend to use this kernel on different machines.

    More information about the internals of the Linux math coprocessor emulation can be found in <file:arch/i386/math-emu/README>.

    If you are not sure, say Y; apart from resulting in a 66 KB bigger kernel, it won't hurt.

• Option: MTRR
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) MTRR (Memory Type Range Register) support

    On Intel P6 family processors (Pentium Pro, Pentium II and later) the Memory Type Range Registers (MTRRs) may be used to control processor access to memory ranges. This is most useful if you have a video (VGA) card on a PCI or AGP bus. Enabling write-combining allows bus write transfers to be combined into a larger transfer before bursting over the PCI/AGP bus. This can increase performance of image write operations 2.5 times or more. Saying Y here creates a /proc/mtrr file which may be used to manipulate your processor's MTRRs. Typically the X server should use this.

    This code has a reasonably generic interface so that similar control registers on other processors can be easily supported as well:

    The Cyrix 6x86, 6x86MX and M II processors have Address Range Registers (ARRs) which provide a similar functionality to MTRRs. For these, the ARRs are used to emulate the MTRRs. The AMD K6-2 (stepping 8 and above) and K6-3 processors have two MTRRs. The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. All of these processors are supported by this code and it makes sense to say Y here if you have one of them.

    Saying Y here also fixes a problem with buggy SMP BIOSes which only set the MTRRs for the boot CPU and not for the secondary CPUs. This can lead to all sorts of problems, so it's good to say Y here.

    You can safely say Y even if your machine doesn't have MTRRs, you'll just add about 9 KB to your kernel.

    See <file:Documentation/mtrr.txt> for more information.

• Option: EFI
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Boot from EFI support (EXPERIMENTAL)
  • depends on ACPI
  • default n

enables the kernel to boot on EFI platforms using configuration information passed to it from the firmware. also enables the kernel to use any EFI runtime services that are (such as the EFI variable services).

option is only useful on systems that have EFI firmware will result in a kernel image that is ~8k larger. In addition, must use the latest ELILO loader available at <http://elilo.sourceforge.net> in order to take advantage of initialization using EFI information (neither GRUB nor LILO know about EFI). However, even with this option, the resultant should continue to boot on existing non-EFI platforms.

• Option: IRQBALANCE
  • Kernel Versions: 2.6.15.6 ...bool Enable kernel irq balancing
  • depends on SMP && X86_IO_APIC
  • default y

    The default yes will allow the kernel to do irq load balancing. Saying no will keep the kernel from doing irq load balancing.

turning this on wastes a bunch of space.

Summit needs it only when NUMA is on

• Option: BOOT_IOREMAP
  • Kernel Versions: 2.6.15.6 ...
  • (on/off)
  • depends on (((X86_SUMMIT || X86_GENERICARCH) && NUMA) || (X86 && EFI))
  • default y

• Option: REGPARM
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Use register arguments (EXPERIMENTAL)
  • depends on EXPERIMENTAL
  • default n

the kernel with -mregparm=3. This uses a different ABI passes the first three arguments of a function call in registers. will probably break binary only modules.

feature is only enabled for gcc-3.0 and later - earlier compilers incorrect output with certain kernel constructs when -mregparm=3 is used.

• Option: SECCOMP
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) Enable seccomp to safely compute untrusted bytecode
  • depends on PROC_FS
  • default y

    This kernel feature is useful for number crunching applications that may need to compute untrusted bytecode during their execution. By using pipes or other transports made available to the process as file descriptors supporting the read/write syscalls, it's possible to isolate those applications in their own address space using seccomp. Once seccomp is enabled via /proc/<pid>/seccomp, it cannot be disabled and the task is only allowed to execute a few safe syscalls defined by each seccomp mode.

    If unsure, say Y. Only embedded should say N here.

• Option: Howto configure the Linux kernel/kernel.hz

• Option: PHYSICAL_START
  • Kernel Versions: 2.6.15.6 ...

"Physical address where the kernel is loaded" if EMBEDDED

• • default "0x100000"

    This gives the physical address where the kernel is loaded. Primarily used in the case of kexec on panic where the fail safe kernel needs to run at a different address than the panic-ed kernel.

    Don't change this unless you know what you are doing.

• Option: KEXEC
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) kexec system call (EXPERIMENTAL)
  • depends on EXPERIMENTAL

    kexec is a system call that implements the ability to shutdown your current kernel, and to start another kernel. It is like a reboot but it is indepedent of the system firmware. And like a reboot you can start any kernel with it, not just Linux.

    The name comes from the similarity to the exec system call.

    It is an ongoing process to be certain the hardware in a machine is properly shutdown, so do not be surprised if this code does not initially work for you. It may help to enable device hotplugging support. As of this writing the exact hardware interface is strongly in flux, so no good recommendation can be made.

• Option: CRASH_DUMP
  • Kernel Versions: 2.6.15.6 ...
  • (on/off) kernel crash dumps (EXPERIMENTAL)
  • depends on EMBEDDED
  • depends on EXPERIMENTAL
  • depends on HIGHMEM

    Generate crash dump after being started by kexec.