Section 9.6. CPU Options

9.6. CPU Options

These options control a wide range of behavior regarding timing, processor use in multiprocessor systems, and other processor issues.

Override level 2 CPU cache size detection.

cachesize= n

Sometimes CPU hardware bugs make them report the cache size incorrectly. The kernel will attempt to work around and fix known problems with most CPUs, but for some CPUs it is not possible to determine what the correct size should be. This option provides an override for these situations. n is measured in bytes.

Set the loops per jiffy.

lpg= n

Specify the loops per jiffy that should be used by the kernel, and thus have the kernel avoid the time-consuming boot-time autodetection of this value. If n is 0, the value will be autodetected as usual.

On SMP systems, this value will be set on all CPUs, which might cause problems if the different CPUs need different settings. An incorrect value will cause incorrect delays in the kernel, which can lead to unpredictable I/O errors and other breakage. Although unlikely, in extreme cases this might damage your hardware.

Set the NMI watchdog value.

nmi_watchdog=[0|1|2|3]

This is a debugging feature that allows the user to override the default nonmaskable interrupt (NMI) watchdog value. 0 specifies that no NMI watchdog should be used. 1 specifies that the APIC should be used if present. 2 specifies that the local APIC should be used if present. 3 means that the NMI watchdog is invalid, so do not use it.

Always use the 387 emulation library.

Always use the 387 math emulation library, even if a 387 math coprocessor is present in the system.

Disable x86 floating-point save and restore.

Disable the x86 floating-point extended register save and restore. The kernel will save only legacy floating-point registers on a task switch.

Do not use the

HLT

instruction.

This option is available because the HLT instruction does not work correctly for some x86 processors. This option tells the kernel not to use the instruction.

Enable the machine check exception feature.

Some processors can check for machine errors (usually errors in the hardware). This option turns this subsystem on, if it has been built into the kernel configuration.

Disable the machine check exception feature.

This option turns the subsystem off.

Disable x86 SYSENTER/SYSEXIT support.

Disable x86 SYSENTER/SYSEXIT support in the kernel. This can cause some system calls to take longer.

Run as a single-processor machine.

Tell an SMP kernel to act as a uniprocessor kernel, even on a multiprocessor machine.

Disable the time stamp counter.

Disable the timestamp counter hardware in the system, if present.

Maximum number of CPUs to use.

maxcpus= n

Specify the maximum number of processors that a SMP kernel should use, even if there are more processors present in the system.