Determining system capabilities

Overview

Obtain information about parameters related to processor availability, cache size, and performance-level characteristics on the system by using the sysctlbyname function. These parameters provide details about your system that can aid in tuning performance. For example, you can obtain the count of the highest-performing processor cores to spawn a worker thread for each core. Or you can determine the size of the L2 cache and the number of processor cores that share it to perform software cache-blocking optimization.

Determine processor characteristics

The system enables a processor core when it’s powered on and available for thread scheduling. Each logical processor core executes a software thread that the operating system manages. On systems where the number of logical processor cores exceeds the number of physical processor cores, two or more logical processor cores share a physical core through simultaneous multithreading (SMT). The following parameters provide processor availability information about the system on chip (SoC):

hw.activecpu

The number of enabled logical processor cores in the SoC. This is an alias of hw.logicalcpu.

hw.ncpu

The number of logical processor cores in the SoC. This is an alias of hw.logicalcpu_max.

hw.logicalcpu

The number of enabled logical processor cores in the SoC. This is an alias of hw.activecpu.

hw.logicalcpu_max

The number of logical processor cores in the SoC. This is an alias of hw.ncpu.

hw.physicalcpu

The number of enabled physical processor cores in the SoC.

hw.physicalcpu_max

The number of physical processor cores in the SoC.

Determine system topology

The following parameters provide processor core performance-level information. First, determine the number of types of processor cores with hw.nperflevels. Then, for each of the parameters, replace N with a number between 0 and the number of performance levels minus one. Lower values of N indicate higher-performance core types.

hw.nperflevels

The number of types of general purpose processor cores in the SoC.

hw.perflevelN.cpusperl2

For processor cores of performance level N, the number of cores that share an L2 cache.

hw.perflevelN.cpusperl3

For processor cores of performance level N, the number of cores that share an L3 cache.

hw.perflevelN.l1dcachesize

For processor cores of performance level N, the size in bytes of the L1 data cache.

hw.perflevelN.l1icachesize

For processor cores of performance level N, the size in bytes of the L1 instruction cache.

hw.perflevelN.l2cachesize

For processor cores of performance level N, the size in bytes of the L2 cache.

hw.perflevelN.l3cachesize

For processor cores of performance level N, the size in bytes of the L3 cache.

hw.perflevelN.logicalcpu

For processor cores of performance level N, the number of enabled logical cores in the SoC.

hw.perflevelN.logicalcpu_max

For processor cores of performance level N, the number of logical cores in the SoC.

hw.perflevelN.physicalcpu

For processor cores of performance level N, the number of enabled physical cores in the SoC.

hw.perflevelN.physicalcpu_max

For processor cores of performance level N, the number of physical cores in the SoC.

Querying the following parameters is equivalent to querying the per-performance-level information for the least performant core. For example, hw.l1dcachesize is equivalent to hw.perflevel[N].l1dcachesize, where N is hw.nperflevels minus one.

hw.l1dcachesize

The size in bytes of the L1 data cache.

hw.l1icachesize

The size in bytes of the L1 instruction cache.

hw.l2cachesize

The size in bytes of the L2 cache.

hw.l3cachesize

The size in bytes of the L3 cache.

Determine memory sizes

The following parameters provide cache line, memory, and page size information:

hw.cachelinesize

The size in bytes of the system cache line.

hw.memsize

The size in bytes of dynamic RAM.

hw.pagesize

The size in bytes of a virtual memory page.

See Also

Parameters

• Determining Instruction Set Characteristics