Gaudi::Timers::RdtscClock< Precision > Class Template Reference

A std::chrono compatible Clock using rdtsc as its timing source. More...

#include <Gaudi/Timers/RdtscClock.h>

Public Types
typedef Precision::rep	rep
typedef Precision::period	period
typedef std::chrono::duration< rep, period >	duration
typedef std::chrono::time_point< RdtscClock >	time_point

Static Public Member Functions
static rep	calibrate () noexcept
	Calibrate the RDTSC clock against wall time. More...
static time_point	now () noexcept

Static Public Attributes
static constexpr bool	is_steady {true}

Static Private Member Functions
static rep	ticks_per_unit () noexcept
static rep	do_calibrate () noexcept

Detailed Description

template<typename Precision = std::chrono::microseconds>
class Gaudi::Timers::RdtscClock< Precision >

A std::chrono compatible Clock using rdtsc as its timing source.

This clock is not directly related to wall time but meant as a low-overhead time interval measurement. The Precision template parameter determines the internal precision of the clock (e.g. std::milli, std::micro). On first invocation of now() the timer is calibrated against a wall-time clock, which will have an overhead of several milliseconds. This can be avoided by calling calibrate() explicitly before the first measurement.

Definition at line 23 of file RdtscClock.h.

Member Typedef Documentation

duration

template<typename Precision = std::chrono::microseconds>

typedef std::chrono::duration<rep, period> Gaudi::Timers::RdtscClock< Precision >::duration

Definition at line 28 of file RdtscClock.h.

period

template<typename Precision = std::chrono::microseconds>

typedef Precision::period Gaudi::Timers::RdtscClock< Precision >::period

Definition at line 27 of file RdtscClock.h.

rep

template<typename Precision = std::chrono::microseconds>

typedef Precision::rep Gaudi::Timers::RdtscClock< Precision >::rep

Definition at line 26 of file RdtscClock.h.

time_point

template<typename Precision = std::chrono::microseconds>

typedef std::chrono::time_point<RdtscClock> Gaudi::Timers::RdtscClock< Precision >::time_point

Definition at line 29 of file RdtscClock.h.

Member Function Documentation

calibrate()

template<typename Precision = std::chrono::microseconds>

static rep Gaudi::Timers::RdtscClock< Precision >::calibrate ( )

inlinestaticnoexcept

Calibrate the RDTSC clock against wall time.

Definition at line 39 of file RdtscClock.h.

{ return ticks_per_unit(); }

do_calibrate()

template<typename Precision = std::chrono::microseconds>

static rep Gaudi::Timers::RdtscClock< Precision >::do_calibrate ( )

inlinestaticprivatenoexcept

Definition at line 49 of file RdtscClock.h.

                                         {
        // Calibration time and conversion factor to unit of Precision
        static constexpr auto calibTime = std::chrono::milliseconds( 100 );
        static constexpr auto toPrec    = std::ratio_divide<std::milli, period>::num;

        // Calibrate against wall clock
        auto t1_ref = std::chrono::high_resolution_clock::now();
        auto t1     = __rdtsc();
        std::this_thread::sleep_for( calibTime );
        auto t2     = __rdtsc();
        auto t2_ref = std::chrono::high_resolution_clock::now();

        // Calculate ticks per unit of Precision
        auto dt_ref         = std::chrono::duration_cast<std::chrono::milliseconds>( t2_ref - t1_ref ).count();
        rep  ticks_per_unit = ( t2 - t1 ) / ( dt_ref * toPrec );

        return ticks_per_unit;
      }

now()

template<typename Precision = std::chrono::microseconds>

static time_point Gaudi::Timers::RdtscClock< Precision >::now ( )

inlinestaticnoexcept

Definition at line 41 of file RdtscClock.h.

{ return time_point{duration( __rdtsc() / ticks_per_unit() )}; }

ticks_per_unit()

template<typename Precision = std::chrono::microseconds>

static rep Gaudi::Timers::RdtscClock< Precision >::ticks_per_unit ( )

inlinestaticprivatenoexcept

Definition at line 44 of file RdtscClock.h.

                                           {
        static rep ticks_per_unit = do_calibrate(); // local static guarantees thread-safety
        return ticks_per_unit;
      }

Member Data Documentation

is_steady

template<typename Precision = std::chrono::microseconds>

constexpr bool Gaudi::Timers::RdtscClock< Precision >::is_steady {true}

static

Definition at line 31 of file RdtscClock.h.

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The documentation for this class was generated from the following file:

• GaudiKernel/Gaudi/Timers/RdtscClock.h