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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_pitEnforces the usage of the PIT if set, otherwise the processor infos are queried, at first.
Returns
Number of TSC ticks per milliseconds
Optional:
Implement calibration via PIT (in the local function ticksByPit()). For testing, it might be useful to compare the return values with different values of use_pit. The returned values should be similar :)

◆ available()

bool TSC::available ( Instruction  instruction = RDTSC)

Check availability of TSC.

Parameters
instructionTest 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
deltaDelta between two timestamps
Returns
Equivalent time in nanoseconds
Optional:
Implement conversion

◆ 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
uswaiting time in microseconds
Optional:
Implement conversion

◆ 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
instructionInstruction(s) used to read timestamp counter
Returns
Timestamp in TSC ticks

Constant Documentation

◆ ticks_value

uint32_t TSC::ticks_value = 0
static