libcpuid  0.2.2
Data Structures | Macros | Typedefs | Enumerations | Functions
LibCPUID

Data Structures

struct  cpu_raw_data_t
 Contains just the raw CPUID data. More...
 
struct  cpu_id_t
 This contains the recognized CPU features/info. More...
 
struct  cpu_mark_t
 Internal structure, used in cpu_tsc_mark, cpu_tsc_unmark and cpu_clock_by_mark. More...
 
struct  cpu_list_t
 a structure that holds a list of processor names More...
 

Macros

#define NUM_CPU_VENDORS   NUM_CPU_VENDORS
 
#define CPU_INVALID_VALUE   0x3fffffff
 

Typedefs

typedef void(* libcpuid_warn_fn_t) (const char *msg)
 

Enumerations

enum  cpu_vendor_t {
  VENDOR_INTEL = 0, VENDOR_AMD, VENDOR_CYRIX, VENDOR_NEXGEN,
  VENDOR_TRANSMETA, VENDOR_UMC, VENDOR_CENTAUR, VENDOR_RISE,
  VENDOR_SIS, VENDOR_NSC, NUM_CPU_VENDORS, VENDOR_UNKNOWN = -1
}
 CPU vendor, as guessed from the Vendor String. More...
 
enum  cpu_feature_t {
  CPU_FEATURE_FPU = 0, CPU_FEATURE_VME, CPU_FEATURE_DE, CPU_FEATURE_PSE,
  CPU_FEATURE_TSC, CPU_FEATURE_MSR, CPU_FEATURE_PAE, CPU_FEATURE_MCE,
  CPU_FEATURE_CX8, CPU_FEATURE_APIC, CPU_FEATURE_MTRR, CPU_FEATURE_SEP,
  CPU_FEATURE_PGE, CPU_FEATURE_MCA, CPU_FEATURE_CMOV, CPU_FEATURE_PAT,
  CPU_FEATURE_PSE36, CPU_FEATURE_PN, CPU_FEATURE_CLFLUSH, CPU_FEATURE_DTS,
  CPU_FEATURE_ACPI, CPU_FEATURE_MMX, CPU_FEATURE_FXSR, CPU_FEATURE_SSE,
  CPU_FEATURE_SSE2, CPU_FEATURE_SS, CPU_FEATURE_HT, CPU_FEATURE_TM,
  CPU_FEATURE_IA64, CPU_FEATURE_PBE, CPU_FEATURE_PNI, CPU_FEATURE_PCLMUL,
  CPU_FEATURE_DTS64, CPU_FEATURE_MONITOR, CPU_FEATURE_DS_CPL, CPU_FEATURE_VMX,
  CPU_FEATURE_SMX, CPU_FEATURE_EST, CPU_FEATURE_TM2, CPU_FEATURE_SSSE3,
  CPU_FEATURE_CID, CPU_FEATURE_CX16, CPU_FEATURE_XTPR, CPU_FEATURE_PDCM,
  CPU_FEATURE_DCA, CPU_FEATURE_SSE4_1, CPU_FEATURE_SSE4_2, CPU_FEATURE_SYSCALL,
  CPU_FEATURE_XD, CPU_FEATURE_MOVBE, CPU_FEATURE_POPCNT, CPU_FEATURE_AES,
  CPU_FEATURE_XSAVE, CPU_FEATURE_OSXSAVE, CPU_FEATURE_AVX, CPU_FEATURE_MMXEXT,
  CPU_FEATURE_3DNOW, CPU_FEATURE_3DNOWEXT, CPU_FEATURE_NX, CPU_FEATURE_FXSR_OPT,
  CPU_FEATURE_RDTSCP, CPU_FEATURE_LM, CPU_FEATURE_LAHF_LM, CPU_FEATURE_CMP_LEGACY,
  CPU_FEATURE_SVM, CPU_FEATURE_ABM, CPU_FEATURE_MISALIGNSSE, CPU_FEATURE_SSE4A,
  CPU_FEATURE_3DNOWPREFETCH, CPU_FEATURE_OSVW, CPU_FEATURE_IBS, CPU_FEATURE_SSE5,
  CPU_FEATURE_SKINIT, CPU_FEATURE_WDT, CPU_FEATURE_TS, CPU_FEATURE_FID,
  CPU_FEATURE_VID, CPU_FEATURE_TTP, CPU_FEATURE_TM_AMD, CPU_FEATURE_STC,
  CPU_FEATURE_100MHZSTEPS, CPU_FEATURE_HWPSTATE, CPU_FEATURE_CONSTANT_TSC, CPU_FEATURE_XOP,
  CPU_FEATURE_FMA3, CPU_FEATURE_FMA4, CPU_FEATURE_TBM, CPU_FEATURE_F16C,
  CPU_FEATURE_RDRAND, CPU_FEATURE_X2APIC, CPU_FEATURE_CPB, CPU_FEATURE_APERFMPERF,
  CPU_FEATURE_PFI, CPU_FEATURE_PA, CPU_FEATURE_AVX2, CPU_FEATURE_BMI1,
  CPU_FEATURE_BMI2, CPU_FEATURE_HLE, CPU_FEATURE_RTM, CPU_FEATURE_AVX512F,
  CPU_FEATURE_AVX512DQ, CPU_FEATURE_AVX512PF, CPU_FEATURE_AVX512ER, CPU_FEATURE_AVX512CD,
  CPU_FEATURE_SHA_NI, CPU_FEATURE_AVX512BW, CPU_FEATURE_AVX512VL, NUM_CPU_FEATURES
}
 CPU feature identifiers. More...
 
enum  cpu_hint_t { CPU_HINT_SSE_SIZE_AUTH = 0, NUM_CPU_HINTS }
 CPU detection hints identifiers. More...
 
enum  cpu_error_t {
  ERR_OK = 0, ERR_NO_CPUID = -1, ERR_NO_RDTSC = -2, ERR_NO_MEM = -3,
  ERR_OPEN = -4, ERR_BADFMT = -5, ERR_NOT_IMP = -6, ERR_CPU_UNKN = -7,
  ERR_NO_RDMSR = -8, ERR_NO_DRIVER = -9, ERR_NO_PERMS = -10, ERR_EXTRACT = -11,
  ERR_HANDLE = -12, ERR_INVMSR = -13, ERR_INVCNB = -14, ERR_HANDLE_R = -15,
  ERR_INVRANGE = -16
}
 Describes common library error codes. More...
 
enum  cpu_msrinfo_request_t {
  INFO_MPERF, INFO_APERF, INFO_CUR_MULTIPLIER, INFO_MAX_MULTIPLIER,
  INFO_TEMPERATURE, INFO_THROTTLING, INFO_VOLTAGE, INFO_BCLK
}
 

Functions

int cpuid_get_total_cpus (void)
 Returns the total number of CPUs even if CPUID is not present. More...
 
int cpuid_present (void)
 Checks if the CPUID instruction is supported. More...
 
void cpu_exec_cpuid (uint32_t eax, uint32_t *regs)
 Executes the CPUID instruction. More...
 
void cpu_exec_cpuid_ext (uint32_t *regs)
 Executes the CPUID instruction with the given input registers. More...
 
int cpuid_get_raw_data (struct cpu_raw_data_t *data)
 Obtains the raw CPUID data from the current CPU. More...
 
int cpuid_serialize_raw_data (struct cpu_raw_data_t *data, const char *filename)
 Writes the raw CPUID data to a text file. More...
 
int cpuid_deserialize_raw_data (struct cpu_raw_data_t *data, const char *filename)
 Reads raw CPUID data from file. More...
 
int cpu_identify (struct cpu_raw_data_t *raw, struct cpu_id_t *data)
 Identifies the CPU. More...
 
const char * cpu_feature_str (cpu_feature_t feature)
 Returns the short textual representation of a CPU flag. More...
 
const char * cpuid_error (void)
 Returns textual description of the last error. More...
 
void cpu_rdtsc (uint64_t *result)
 Executes RDTSC. More...
 
void cpu_tsc_mark (struct cpu_mark_t *mark)
 Store TSC and timing info. More...
 
void cpu_tsc_unmark (struct cpu_mark_t *mark)
 Calculate TSC and timing difference. More...
 
int cpu_clock_by_mark (struct cpu_mark_t *mark)
 Calculates the CPU clock. More...
 
int cpu_clock_by_os (void)
 Returns the CPU clock, as reported by the OS. More...
 
int cpu_clock_measure (int millis, int quad_check)
 Measure the CPU clock frequency. More...
 
int cpu_clock_by_ic (int millis, int runs)
 Measure the CPU clock frequency using instruction-counting. More...
 
int cpu_clock (void)
 Get the CPU clock frequency (all-in-one method) More...
 
const char * cpuid_lib_version (void)
 Returns the libcpuid version. More...
 
libcpuid_warn_fn_t cpuid_set_warn_function (libcpuid_warn_fn_t warn_fun)
 Sets the warning print function. More...
 
void cpuid_set_verbosiness_level (int level)
 Sets the verbosiness level. More...
 
cpu_vendor_t cpuid_get_vendor (void)
 Obtains the CPU vendor from CPUID from the current CPU. More...
 
void cpuid_get_cpu_list (cpu_vendor_t vendor, struct cpu_list_t *list)
 Gets a list of all known CPU names from a specific vendor. More...
 
void cpuid_free_cpu_list (struct cpu_list_t *list)
 Frees a CPU list. More...
 
struct msr_driver_t * cpu_msr_driver_open (void)
 Starts/opens a driver, needed to read MSRs (Model Specific Registers) More...
 
struct msr_driver_t * cpu_msr_driver_open_core (unsigned core_num)
 Similar to cpu_msr_driver_open, but accept one parameter. More...
 
int cpu_rdmsr (struct msr_driver_t *handle, uint32_t msr_index, uint64_t *result)
 Reads a Model-Specific Register (MSR) More...
 
int cpu_rdmsr_range (struct msr_driver_t *handle, uint32_t msr_index, uint8_t highbit, uint8_t lowbit, uint64_t *result)
 Similar to cpu_rdmsr, but extract a range of bits. More...
 
int cpu_msrinfo (struct msr_driver_t *handle, cpu_msrinfo_request_t which)
 Reads extended CPU information from Model-Specific Registers. More...
 
int cpu_msr_driver_close (struct msr_driver_t *handle)
 Closes an open MSR driver. More...
 

Detailed Description

Enumeration Type Documentation

Describes common library error codes.

Enumerator
ERR_OK 

"No error"

ERR_NO_CPUID 

"CPUID instruction is not supported"

ERR_NO_RDTSC 

"RDTSC instruction is not supported"

ERR_NO_MEM 

"Memory allocation failed"

ERR_OPEN 

"File open operation failed"

ERR_BADFMT 

"Bad file format"

ERR_NOT_IMP 

"Not implemented"

ERR_CPU_UNKN 

"Unsupported processor"

ERR_NO_RDMSR 

"RDMSR instruction is not supported"

ERR_NO_DRIVER 

"RDMSR driver error (generic)"

ERR_NO_PERMS 

"No permissions to install RDMSR driver"

ERR_EXTRACT 

"Cannot extract RDMSR driver (read only media?)"

ERR_HANDLE 

"Bad handle"

ERR_INVMSR 

"Invalid MSR"

ERR_INVCNB 

"Invalid core number"

ERR_HANDLE_R 

"Error on handle read"

ERR_INVRANGE 

"Invalid given range"

CPU feature identifiers.

Usage:

1 ...
2 struct cpu_raw_data_t raw;
3 struct cpu_id_t id;
4 if (cpuid_get_raw_data(&raw) == 0 && cpu_identify(&raw, &id) == 0) {
5  if (id.flags[CPU_FEATURE_SSE2]) {
6  // The CPU has SSE2...
7  ...
8  } else {
9  // no SSE2
10  }
11 } else {
12  // processor cannot be determined.
13 }
Enumerator
CPU_FEATURE_FPU 

Floating point unit

CPU_FEATURE_VME 

Virtual mode extension

CPU_FEATURE_DE 

Debugging extension

CPU_FEATURE_PSE 

Page size extension

CPU_FEATURE_TSC 

Time-stamp counter

CPU_FEATURE_MSR 

Model-specific regsisters, RDMSR/WRMSR supported

CPU_FEATURE_PAE 

Physical address extension

CPU_FEATURE_MCE 

Machine check exception

CPU_FEATURE_CX8 

CMPXCHG8B instruction supported

CPU_FEATURE_APIC 

APIC support

CPU_FEATURE_MTRR 

Memory type range registers

CPU_FEATURE_SEP 

SYSENTER / SYSEXIT instructions supported

CPU_FEATURE_PGE 

Page global enable

CPU_FEATURE_MCA 

Machine check architecture

CPU_FEATURE_CMOV 

CMOVxx instructions supported

CPU_FEATURE_PAT 

Page attribute table

CPU_FEATURE_PSE36 

36-bit page address extension

CPU_FEATURE_PN 

Processor serial # implemented (Intel P3 only)

CPU_FEATURE_CLFLUSH 

CLFLUSH instruction supported

CPU_FEATURE_DTS 

Debug store supported

CPU_FEATURE_ACPI 

ACPI support (power states)

CPU_FEATURE_MMX 

MMX instruction set supported

CPU_FEATURE_FXSR 

FXSAVE / FXRSTOR supported

CPU_FEATURE_SSE 

Streaming-SIMD Extensions (SSE) supported

CPU_FEATURE_SSE2 

SSE2 instructions supported

CPU_FEATURE_SS 

Self-snoop

CPU_FEATURE_HT 

Hyper-threading supported (but might be disabled)

CPU_FEATURE_TM 

Thermal monitor

CPU_FEATURE_IA64 

IA64 supported (Itanium only)

CPU_FEATURE_PBE 

Pending-break enable

CPU_FEATURE_PNI 

PNI (SSE3) instructions supported

CPU_FEATURE_PCLMUL 

PCLMULQDQ instruction supported

CPU_FEATURE_DTS64 

64-bit Debug store supported

CPU_FEATURE_MONITOR 

MONITOR / MWAIT supported

CPU_FEATURE_DS_CPL 

CPL Qualified Debug Store

CPU_FEATURE_VMX 

Virtualization technology supported

CPU_FEATURE_SMX 

Safer mode exceptions

CPU_FEATURE_EST 

Enhanced SpeedStep

CPU_FEATURE_TM2 

Thermal monitor 2

CPU_FEATURE_SSSE3 

SSSE3 instructionss supported (this is different from SSE3!)

CPU_FEATURE_CID 

Context ID supported

CPU_FEATURE_CX16 

CMPXCHG16B instruction supported

CPU_FEATURE_XTPR 

Send Task Priority Messages disable

CPU_FEATURE_PDCM 

Performance capabilities MSR supported

CPU_FEATURE_DCA 

Direct cache access supported

CPU_FEATURE_SSE4_1 

SSE 4.1 instructions supported

CPU_FEATURE_SSE4_2 

SSE 4.2 instructions supported

CPU_FEATURE_SYSCALL 

SYSCALL / SYSRET instructions supported

CPU_FEATURE_XD 

Execute disable bit supported

CPU_FEATURE_MOVBE 

MOVBE instruction supported

CPU_FEATURE_POPCNT 

POPCNT instruction supported

CPU_FEATURE_AES 

AES* instructions supported

CPU_FEATURE_XSAVE 

XSAVE/XRSTOR/etc instructions supported

CPU_FEATURE_OSXSAVE 

non-privileged copy of OSXSAVE supported

CPU_FEATURE_AVX 

Advanced vector extensions supported

CPU_FEATURE_MMXEXT 

AMD MMX-extended instructions supported

CPU_FEATURE_3DNOW 

AMD 3DNow! instructions supported

CPU_FEATURE_3DNOWEXT 

AMD 3DNow! extended instructions supported

CPU_FEATURE_NX 

No-execute bit supported

CPU_FEATURE_FXSR_OPT 

FFXSR: FXSAVE and FXRSTOR optimizations

CPU_FEATURE_RDTSCP 

RDTSCP instruction supported (AMD-only)

CPU_FEATURE_LM 

Long mode (x86_64/EM64T) supported

CPU_FEATURE_LAHF_LM 

LAHF/SAHF supported in 64-bit mode

CPU_FEATURE_CMP_LEGACY 

core multi-processing legacy mode

CPU_FEATURE_SVM 

AMD Secure virtual machine

CPU_FEATURE_ABM 

LZCNT instruction support

CPU_FEATURE_MISALIGNSSE 

Misaligned SSE supported

CPU_FEATURE_SSE4A 

SSE 4a from AMD

CPU_FEATURE_3DNOWPREFETCH 

PREFETCH/PREFETCHW support

CPU_FEATURE_OSVW 

OS Visible Workaround (AMD)

CPU_FEATURE_IBS 

Instruction-based sampling

CPU_FEATURE_SSE5 

SSE 5 instructions supported (deprecated, will never be 1)

CPU_FEATURE_SKINIT 

SKINIT / STGI supported

CPU_FEATURE_WDT 

Watchdog timer support

CPU_FEATURE_TS 

Temperature sensor

CPU_FEATURE_FID 

Frequency ID control

CPU_FEATURE_VID 

Voltage ID control

CPU_FEATURE_TTP 

THERMTRIP

CPU_FEATURE_TM_AMD 

AMD-specified hardware thermal control

CPU_FEATURE_STC 

Software thermal control

CPU_FEATURE_100MHZSTEPS 

100 MHz multiplier control

CPU_FEATURE_HWPSTATE 

Hardware P-state control

CPU_FEATURE_CONSTANT_TSC 

TSC ticks at constant rate

CPU_FEATURE_XOP 

The XOP instruction set (same as the old CPU_FEATURE_SSE5)

CPU_FEATURE_FMA3 

The FMA3 instruction set

CPU_FEATURE_FMA4 

The FMA4 instruction set

CPU_FEATURE_TBM 

Trailing bit manipulation instruction support

CPU_FEATURE_F16C 

16-bit FP convert instruction support

CPU_FEATURE_RDRAND 

RdRand instruction

CPU_FEATURE_X2APIC 

x2APIC, APIC_BASE.EXTD, MSRs 0000_0800h...0000_0BFFh 64-bit ICR (+030h but not +031h), no DFR (+00Eh), SELF_IPI (+040h) also see standard level 0000_000Bh

CPU_FEATURE_CPB 

Core performance boost

CPU_FEATURE_APERFMPERF 

MPERF/APERF MSRs support

CPU_FEATURE_PFI 

Processor Feedback Interface support

CPU_FEATURE_PA 

Processor accumulator

CPU_FEATURE_AVX2 

AVX2 instructions

CPU_FEATURE_BMI1 

BMI1 instructions

CPU_FEATURE_BMI2 

BMI2 instructions

CPU_FEATURE_HLE 

Hardware Lock Elision prefixes

CPU_FEATURE_RTM 

Restricted Transactional Memory instructions

CPU_FEATURE_AVX512F 

AVX-512 Foundation

CPU_FEATURE_AVX512DQ 

AVX-512 Double/Quad granular insns

CPU_FEATURE_AVX512PF 

AVX-512 Prefetch

CPU_FEATURE_AVX512ER 

AVX-512 Exponential/Reciprocal

CPU_FEATURE_AVX512CD 

AVX-512 Conflict detection

CPU_FEATURE_SHA_NI 

SHA-1/SHA-256 instructions

CPU_FEATURE_AVX512BW 

AVX-512 Byte/Word granular insns

CPU_FEATURE_AVX512VL 

AVX-512 128/256 vector length extensions

enum cpu_hint_t

CPU detection hints identifiers.

Usage: similar to the flags usage

Enumerator
CPU_HINT_SSE_SIZE_AUTH 

SSE unit size is authoritative (not only a Family/Model guesswork, but based on an actual CPUID bit)

Enumerator
INFO_MPERF 

Maximum performance frequency clock. This is a counter, which increments as a proportion of the actual processor speed.

INFO_APERF 

Actual performance frequency clock. This accumulates the core clock counts when the core is active.

INFO_CUR_MULTIPLIER 

Current CPU:FSB ratio, multiplied by 100. e.g., a CPU:FSB value of 18.5 reads as "1850".

INFO_MAX_MULTIPLIER 

Maxumum CPU:FSB ratio for this CPU, multiplied by 100.

INFO_TEMPERATURE 

The current core temperature in Celsius.

INFO_THROTTLING 

1 if the current logical processor is throttling. 0 if it is running normally.

INFO_VOLTAGE 

The current core voltage in Volt, multiplied by 100.

INFO_BCLK 

The BCLK (base clock) in MHz, multiplied by 100.

CPU vendor, as guessed from the Vendor String.

Enumerator
VENDOR_INTEL 

Intel CPU

VENDOR_AMD 

AMD CPU

VENDOR_CYRIX 

Cyrix CPU

VENDOR_NEXGEN 

NexGen CPU

VENDOR_TRANSMETA 

Transmeta CPU

VENDOR_UMC 

x86 CPU by UMC

VENDOR_CENTAUR 

x86 CPU by IDT

VENDOR_RISE 

x86 CPU by Rise Technology

VENDOR_SIS 

x86 CPU by SiS

VENDOR_NSC 

x86 CPU by National Semiconductor

NUM_CPU_VENDORS 

Valid CPU vendor ids: 0..NUM_CPU_VENDORS - 1

Function Documentation

int cpu_clock ( void  )

Get the CPU clock frequency (all-in-one method)

This is an all-in-one method for getting the CPU clock frequency. It tries to use the OS for that. If the OS doesn't have this info, it uses cpu_clock_measure with 200ms time interval and quadruple checking.

Returns
the CPU clock frequency in MHz. If every possible method fails, the result is -1.
int cpu_clock_by_ic ( int  millis,
int  runs 
)

Measure the CPU clock frequency using instruction-counting.

Parameters
millis- how much time to allocate for each run, in milliseconds
runs- how many runs to perform

The function performs a busy-wait cycle using a known number of "heavy" (SSE) instructions. These instructions run at (more or less guaranteed) 1 IPC rate, so by running a busy loop for a fixed amount of time, and measuring the amount of instructions done, the CPU clock is accurately measured.

Of course, this function is still affected by the power-saving schemes, so the warnings as of cpu_clock_measure() still apply. However, this function is immune to problems with detection, related to the Intel Nehalem's "Turbo" mode, where the internal clock is raised, but the RDTSC rate is unaffected.

The function will run for about (millis * runs) milliseconds. You can make only a single busy-wait run (runs == 1); however, this can be affected by task scheduling (which will break the counting), so allowing more than one run is recommended. As run length is not imperative for accurate readings (e.g., 50ms is sufficient), you can afford a lot of short runs, e.g. 10 runs of 50ms or 20 runs of 25ms.

Recommended values - millis = 50, runs = 4. For more robustness, increase the number of runs.

NOTE: on Bulldozer and later CPUs, the busy-wait cycle runs at 1.4 IPC, thus the results are skewed. This is corrected internally by dividing the resulting value by 1.4. However, this only occurs if the thread is executed on a single CMT module - if there are other threads competing for resources, the results are unpredictable. Make sure you run cpu_clock_by_ic() on a CPU that is free from competing threads, or if there are such threads, they shouldn't exceed the number of modules. On a Bulldozer X8, that means 4 threads.

Returns
the CPU clock frequency in MHz (within some measurement error margin). If SSE is not supported, the result is -1. If the input parameters are incorrect, or some other internal fault is detected, the result is -2.
int cpu_clock_by_mark ( struct cpu_mark_t mark)

Calculates the CPU clock.

Parameters
mark- pointer to a cpu_mark_t structure, which has been initialized with cpu_tsc_mark and later `stopped' with cpu_tsc_unmark.
Note
For reliable results, the marked time interval should be at least about 10 ms.
Returns
the CPU clock frequency, in MHz. Due to measurement error, it will differ from the true value in a few least-significant bits. Accuracy depends on the timing interval - the more, the better. If the timing interval is insufficient, the result is -1. Also, see the comment on cpu_clock_measure for additional issues and pitfalls in using RDTSC for CPU frequency measurements.
int cpu_clock_by_os ( void  )

Returns the CPU clock, as reported by the OS.

This function uses OS-specific functions to obtain the CPU clock. It may differ from the true clock for several reasons:

i) The CPU might be in some power saving state, while the OS reports its full-power frequency, or vice-versa.
ii) In some cases you can raise or lower the CPU frequency with overclocking utilities and the OS will not notice.

Returns
the CPU clock frequency in MHz. If the OS is not (yet) supported or lacks the necessary reporting machinery, the return value is -1
int cpu_clock_measure ( int  millis,
int  quad_check 
)

Measure the CPU clock frequency.

Parameters
millis- How much time to waste in the busy-wait cycle. In millisecs. Useful values 10 - 1000
quad_check- Do a more thorough measurement if nonzero (see the explanation).

The function performs a busy-wait cycle for the given time and calculates the CPU frequency by the difference of the TSC values. The accuracy of the calculation depends on the length of the busy-wait cycle: more is better, but 100ms should be enough for most purposes.

While this will calculate the CPU frequency correctly in most cases, there are several reasons why it might be incorrect:

i) RDTSC doesn't guarantee it will run at the same clock as the CPU. Apparently there aren't CPUs at the moment, but still, there's no guarantee.
ii) The CPU might be in a low-frequency power saving mode, and the CPU might be switched to higher frequency at any time. If this happens during the measurement, the result can be anywhere between the low and high frequencies. Also, if you're interested in the high frequency value only, this function might return the low one instead.
iii) On SMP systems exhibiting TSC drift (see cpu_rdtsc)

the quad_check option will run four consecutive measurements and then return the average of the two most-consistent results. The total runtime of the function will still be `millis' - consider using a bit more time for the timing interval.

Finally, for benchmarking / CPU intensive applications, the best strategy is to use the cpu_tsc_mark() / cpu_tsc_unmark() / cpu_clock_by_mark() method. Begin by mark()-ing about one second after application startup (allowing the power-saving manager to kick in and rise the frequency during that time), then unmark() just before application finishing. The result will most acurately represent at what frequency your app was running.

Returns
the CPU clock frequency in MHz (within some measurement error margin). If RDTSC is not supported, the result is -1.
void cpu_exec_cpuid ( uint32_t  eax,
uint32_t *  regs 
)

Executes the CPUID instruction.

Parameters
eax- the value of the EAX register when executing CPUID
regs- the results will be stored here. regs[0] = EAX, regs[1] = EBX, ...
Note
CPUID will be executed with EAX set to the given value and EBX, ECX, EDX set to zero.
void cpu_exec_cpuid_ext ( uint32_t *  regs)

Executes the CPUID instruction with the given input registers.

Note
This is just a bit more generic version of cpu_exec_cpuid - it allows you to control all the registers.
Parameters
regs- Input/output. Prior to executing CPUID, EAX, EBX, ECX and EDX will be set to regs[0], regs[1], regs[2] and regs[3]. After CPUID, this array will contain the results.
const char* cpu_feature_str ( cpu_feature_t  feature)

Returns the short textual representation of a CPU flag.

Parameters
feature- the feature, whose textual representation is wanted.
Returns
a constant string like "fpu", "tsc", "sse2", etc.
Note
the names of the returned flags are compatible with those from /proc/cpuinfo in Linux, with the exception of `tm_amd'
int cpu_identify ( struct cpu_raw_data_t raw,
struct cpu_id_t data 
)

Identifies the CPU.

Parameters
raw- Input - a pointer to the raw CPUID data, which is obtained either by cpuid_get_raw_data or cpuid_deserialize_raw_data. Can also be NULL, in which case the functions calls cpuid_get_raw_data itself.
data- Output - the decoded CPU features/info is written here.
Note
The function will not fail, even if some of the information cannot be obtained. Even when the CPU is new and thus unknown to libcpuid, some generic info, such as "AMD K9 family CPU" will be written to data.cpu_codename, and most other things, such as the CPU flags, cache sizes, etc. should be detected correctly anyway. However, the function CAN fail, if the CPU is completely alien to libcpuid.
While cpu_identify() and cpuid_get_raw_data() are fast for most purposes, running them several thousand times per second can hamper performance significantly. Specifically, avoid writing "cpu feature checker" wrapping function, which calls cpu_identify and returns the value of some flag, if that function is going to be called frequently.
Returns
zero if successful, and some negative number on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
int cpu_msr_driver_close ( struct msr_driver_t *  handle)

Closes an open MSR driver.

This function unloads the MSR driver opened by cpu_msr_driver_open and frees any resources associated with it.

Parameters
handle- a handle to the MSR reader driver, as created by cpu_msr_driver_open
Returns
zero if successful, and some negative number on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
struct msr_driver_t* cpu_msr_driver_open ( void  )

Starts/opens a driver, needed to read MSRs (Model Specific Registers)

On systems that support it, this function will create a temporary system driver, that has privileges to execute the RDMSR instruction. After the driver is created, you can read MSRs by calling cpu_rdmsr

Returns
a handle to the driver on success, and NULL on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
struct msr_driver_t* cpu_msr_driver_open_core ( unsigned  core_num)

Similar to cpu_msr_driver_open, but accept one parameter.

This function works on certain operating systems (GNU/Linux, FreeBSD)

Parameters
core_numspecify the core number for MSR. The first core number is 0. The last core number is cpuid_get_total_cpus - 1.
Returns
a handle to the driver on success, and NULL on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
int cpu_msrinfo ( struct msr_driver_t *  handle,
cpu_msrinfo_request_t  which 
)

Reads extended CPU information from Model-Specific Registers.

Parameters
handle- a handle to an open MSR driver,
See also
cpu_msr_driver_open
Parameters
which- which info field should be returned. A list of available information entities is listed in the cpu_msrinfo_request_t enum.
Return values
-if the requested information is available for the current processor model, the respective value is returned. if no information is available, or the CPU doesn't support the query, the special value CPU_INVALID_VALUE is returned
int cpu_rdmsr ( struct msr_driver_t *  handle,
uint32_t  msr_index,
uint64_t *  result 
)

Reads a Model-Specific Register (MSR)

If the CPU has MSRs (as indicated by the CPU_FEATURE_MSR flag), you can read a MSR with the given index by calling this function.

There are several prerequisites you must do before reading MSRs: 1) You must ensure the CPU has RDMSR. Check the CPU_FEATURE_MSR flag in cpu_id_t::flags 2) You must ensure that the CPU implements the specific MSR you intend to read. 3) You must open a MSR-reader driver. RDMSR is a privileged instruction and needs ring-0 access in order to work. This temporary driver is created by calling cpu_msr_driver_open

Parameters
handle- a handle to the MSR reader driver, as created by cpu_msr_driver_open
msr_index- the numeric ID of the MSR you want to read
result- a pointer to a 64-bit integer, where the MSR value is stored
Returns
zero if successful, and some negative number on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
int cpu_rdmsr_range ( struct msr_driver_t *  handle,
uint32_t  msr_index,
uint8_t  highbit,
uint8_t  lowbit,
uint64_t *  result 
)

Similar to cpu_rdmsr, but extract a range of bits.

Parameters
handle- a handle to the MSR reader driver, as created by cpu_msr_driver_open
msr_index- the numeric ID of the MSR you want to read
highbit- the high bit in range, must be inferior to 64
lowbit- the low bit in range, must be equal or superior to 0
result- a pointer to a 64-bit integer, where the MSR value is stored
Returns
zero if successful, and some negative number on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
void cpu_rdtsc ( uint64_t *  result)

Executes RDTSC.

The RDTSC (ReaD Time Stamp Counter) instruction gives access to an internal 64-bit counter, which usually increments at each clock cycle. This can be used for various timing routines, and as a very precise clock source. It is set to zero on system startup. Beware that may not increment at the same frequency as the CPU. Consecutive calls of RDTSC are, however, guaranteed to return monotonically-increasing values.

Parameters
result- a pointer to a 64-bit unsigned integer, where the TSC value will be stored
Note
If 100% compatibility is a concern, you must first check if the RDTSC instruction is present (if it is not, your program will crash with "invalid opcode" exception). Only some very old processors (i486, early AMD K5 and some Cyrix CPUs) lack that instruction - they should have become exceedingly rare these days. To verify RDTSC presence, run cpu_identify() and check flags[CPU_FEATURE_TSC].
The monotonically increasing nature of the TSC may be violated on SMP systems, if their TSC clocks run at different rate. If the OS doesn't account for that, the TSC drift may become arbitrary large.
void cpu_tsc_mark ( struct cpu_mark_t mark)

Store TSC and timing info.

This function stores the current TSC value and current time info from a precise OS-specific clock source in the cpu_mark_t structure. The sys_clock field contains time with microsecond resolution. The values can later be used to measure time intervals, number of clocks, FPU frequency, etc.

See also
cpu_rdtsc
Parameters
mark[out] - a pointer to a cpu_mark_t structure
void cpu_tsc_unmark ( struct cpu_mark_t mark)

Calculate TSC and timing difference.

Parameters
mark- input/output: a pointer to a cpu_mark_t sturcture, which has already been initialized by cpu_tsc_mark. The difference in TSC and time will be written here.

This function calculates the TSC and time difference, by obtaining the current TSC and timing values and subtracting the contents of the `mark' structure from them. Results are written in the same structure.

Example:

1 ...
2 struct cpu_mark_t mark;
3 cpu_tsc_mark(&mark);
4 foo();
5 cpu_tsc_unmark(&mark);
6 printf("Foo finished. Executed in %llu cycles and %llu usecs\n",
7  mark.tsc, mark.sys_clock);
8 ...
int cpuid_deserialize_raw_data ( struct cpu_raw_data_t data,
const char *  filename 
)

Reads raw CPUID data from file.

Parameters
data- a pointer to cpu_raw_data_t structure. The deserialized data will be written here.
filename- the path of the file, containing the serialized raw data. If empty, stdin will be used.
Note
This function may fail, if the file is created by different version of the library. Also, see the notes on cpuid_serialize_raw_data.
Returns
zero if successful, and some negative number on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
const char* cpuid_error ( void  )

Returns textual description of the last error.

libcpuid stores an `errno'-style error status, whose description can be obtained with this function.

Note
This function is not thread-safe
See also
cpu_error_t
void cpuid_free_cpu_list ( struct cpu_list_t list)

Frees a CPU list.

This function deletes all the memory associated with a CPU list, as obtained by cpuid_get_cpu_list()

Parameters
list- the list to be free()'d.
void cpuid_get_cpu_list ( cpu_vendor_t  vendor,
struct cpu_list_t list 
)

Gets a list of all known CPU names from a specific vendor.

This function compiles a list of all known CPU (code)names (i.e. the possible values of cpu_id_t::cpu_codename) for the given vendor.

There are about 100 entries for Intel and AMD, and a few for the other vendors. The list is written out in approximate chronological introduction order of the parts.

Parameters
vendorthe vendor to be queried
list[out] the resulting list will be written here. NOTE: As the memory is dynamically allocated, be sure to call cpuid_free_cpu_list() after you're done with the data
See also
cpu_list_t
int cpuid_get_raw_data ( struct cpu_raw_data_t data)

Obtains the raw CPUID data from the current CPU.

Parameters
data- a pointer to cpu_raw_data_t structure
Returns
zero if successful, and some negative number on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
int cpuid_get_total_cpus ( void  )

Returns the total number of CPUs even if CPUID is not present.

Return values
Numberof CPUs available
cpu_vendor_t cpuid_get_vendor ( void  )

Obtains the CPU vendor from CPUID from the current CPU.

Note
The result is cached.
Returns
VENDOR_UNKNOWN if failed, otherwise the CPU vendor type.
See also
cpu_vendor_t
const char* cpuid_lib_version ( void  )

Returns the libcpuid version.

Returns
the string representation of the libcpuid version, like "0.1.1"
int cpuid_present ( void  )

Checks if the CPUID instruction is supported.

Return values
1if CPUID is present
0the CPU doesn't have CPUID.
int cpuid_serialize_raw_data ( struct cpu_raw_data_t data,
const char *  filename 
)

Writes the raw CPUID data to a text file.

Parameters
data- a pointer to cpu_raw_data_t structure
filename- the path of the file, where the serialized data should be written. If empty, stdout will be used.
Note
This is intended primarily for debugging. On some processor, which is not currently supported or not completely recognized by cpu_identify, one can still successfully get the raw data and write it to a file. libcpuid developers can later import this file and debug the detection code as if running on the actual hardware. The file is simple text format of "something=value" pairs. Version info is also written, but the format is not intended to be neither backward- nor forward compatible.
Returns
zero if successful, and some negative number on error. The error message can be obtained by calling cpuid_error.
See also
cpu_error_t
void cpuid_set_verbosiness_level ( int  level)

Sets the verbosiness level.

When the verbosiness level is above zero, some functions might print diagnostic information about what are they doing. The higher the level is, the more detail is printed. Level zero is guaranteed to omit all such output. The output is written using the same machinery as the warnings,

See also
cpuid_set_warn_function()
Parameters
levelthe desired verbosiness level. Useful values 0..2 inclusive
libcpuid_warn_fn_t cpuid_set_warn_function ( libcpuid_warn_fn_t  warn_fun)

Sets the warning print function.

In some cases, the internal libcpuid machinery would like to emit useful debug warnings. By default, these warnings are written to stderr. However, you can set a custom function that will receive those warnings.

Parameters
warn_fun- the warning function you want to set. If NULL, warnings are disabled. The function takes const char* argument.
Returns
the current warning function. You can use the return value to keep the previous warning function and restore it at your discretion.