TSC Namespace Reference

Access to the Timestamp Counter (of the current Core) More...

Enumerations
enum	Instruction {   RDTSC ,   RDTSCP ,   CPUID_RDTSC ,   RDTSCP_CPUID ,   CR0_RDTSC }

Functions
static uint32_t	ticksByProcessorInfo (void)
	Calculate the TSC frequency, if possible.
static uint32_t	ticksByPIT (void)
	Measure the TSC frequency using PIT.
uint32_t	ticks (bool use_pit=false)
	Gather the TSC frequency in ticks per milliseconds.
bool	available (Instruction instruction=RDTSC)
	Check availability of TSC.
uint64_t	nanoseconds (uint64_t delta)
	Convert a timestamp delta value to nanoseconds.
void	delay (uint64_t us)
	Actively wait the provided waiting time.
uint64_t	read (Instruction instruction=RDTSC)
	Reads the current timestamp counter.

Constants
static uint32_t	ticks_value = 0

Detailed Description

Access to the Timestamp Counter (of the current Core)

Intel Manual Vol. 3, 17.17 Time-Stamp Counter

Enumeration Type Documentation

Instruction

enum TSC::Instruction

Enumerator
RDTSC	TSC Read with possible out-of-order execution.
RDTSCP	Pseudo serializing.
CPUID_RDTSC	Serializing (via CPUID) TSC read for begin of benchmark.
RDTSCP_CPUID	Serializing (via CPUID) TSC read for end of benchmark.
CR0_RDTSC	Serializing (via CR0) TSC read for end of benchmark if RDTSCP is not supported.

Function Documentation

ticksByProcessorInfo()

static uint32_t TSC::ticksByProcessorInfo ( void  )

static

Calculate the TSC frequency, if possible.

Note

Does not work in QEMU

Returns

Ticks per millisecond, or 0 if not possible

ticksByPIT()

static uint32_t TSC::ticksByPIT ( void  )

static

Measure the TSC frequency using PIT.

Returns

TSC ticks per millisecond

ticks()

uint32_t TSC::ticks

(

bool

use_pit = false

)

Gather the TSC frequency in ticks per milliseconds.

Parameters

use_pit

Enforces the usage of the PIT if set, otherwise the processor infos are queried, at first.

Returns

Number of TSC ticks per milliseconds

available()

bool TSC::available

(

Instruction

instruction = RDTSC

)

Check availability of TSC.

Parameters

instruction

Test for the (unserialized) RDTSC or pseudo serializing RDTSCP instruction

Returns

true if RDTSC[P] is available

nanoseconds()

uint64_t TSC::nanoseconds

(

uint64_t

delta

)

Convert a timestamp delta value to nanoseconds.

Note

It is necessary to execute TSC::ticks() prior calling this function the first time, since it uses the cached TSC frequency value gathered by ticks() for the calculation.

Parameters

delta

Delta between two timestamps

Returns

Equivalent time in nanoseconds

delay()

void TSC::delay

(

uint64_t

us

)

Actively wait the provided waiting time.

Note

It is necessary to execute TSC::ticks() prior calling this function the first time, since it uses the cached TSC frequency value gathered by ticks() for the calculation.

Parameters

us	waiting time in microseconds

read()

uint64_t TSC::read ( Instruction  instruction = RDTSC )

inline

Reads the current timestamp counter.

While reading the timestamp counter is quite easy, it is difficult to prevent out-of-order execution.

See also

How to Benchmark Code Execution Times on Intel® IA-32 and IA-64 Instruction Set Architectures [benchmark_code_execution.pdf]

Parameters

instruction

Instruction(s) used to read timestamp counter

Returns

Timestamp in TSC ticks

Constant Documentation

ticks_value

uint32_t TSC::ticks_value = 0

static