qpc.cpp

Go to the documentation of this file.

/* Copyright (c) 2010 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * Timer implementation using QueryPerformanceCounter
 */

#include "precompiled.h"
#include "lib/sysdep/os/win/whrt/qpc.h"

#include "lib/sysdep/os/win/whrt/counter.h"

#include "lib/sysdep/os_cpu.h"
#include "lib/sysdep/os/win/win.h"
#include "lib/sysdep/os/win/wutil.h"    // wutil_argv
#include "lib/sysdep/os/win/whrt/pit.h" // PIT_FREQ
#include "lib/sysdep/os/win/whrt/pmt.h" // PMT_FREQ


class CounterQPC : public ICounter
{
public:
    CounterQPC()
        : m_frequency(-1)
    {
    }

    virtual const wchar_t* Name() const
    {
        return L"QPC";
    }

    Status Activate()
    {
        // note: QPC is observed to be universally supported, but the API
        // provides for failure, so play it safe.

        LARGE_INTEGER qpcFreq, qpcValue;
        const BOOL ok1 = QueryPerformanceFrequency(&qpcFreq);
        const BOOL ok2 = QueryPerformanceCounter(&qpcValue);
        if(!ok1 || !ok2)
            WARN_RETURN(ERR::FAIL);
        if(!qpcFreq.QuadPart || !qpcValue.QuadPart)
            WARN_RETURN(ERR::FAIL);

        m_frequency = (i64)qpcFreq.QuadPart;
        return INFO::OK;
    }

    void Shutdown()
    {
    }

    bool IsSafe() const
    {
        // note: we have separate modules that directly access some of the
        // counters potentially used by QPC. disabling the redundant counters
        // would be ugly (increased coupling). instead, we'll make sure our
        // implementations could (if necessary) coexist with QPC, but it
        // shouldn't come to that since only one counter is needed/used.

        // the PIT is entirely safe (even if annoyingly slow to read)
        if(m_frequency == PIT_FREQ)
            return true;

        // the PMT is generally safe (see discussion in CounterPmt::IsSafe),
        // but older QPC implementations had problems with 24-bit rollover.
        // "System clock problem can inflate benchmark scores"
        // (http://www.lionbridge.com/bi/cont2000/200012/perfcnt.asp ; no longer
        // online, nor findable in Google Cache / archive.org) tells of
        // incorrect values every 4.6 seconds (i.e. 24 bits @ 3.57 MHz) unless
        // the timer is polled in the meantime. fortunately, this is guaranteed
        // by our periodic updates (which come at least that often).
        if(m_frequency == PMT_FREQ)
            return true;

        // the TSC has been known to be buggy (even mentioned in MSDN). it is
        // used on MP HAL systems and can be detected by comparing QPF with the
        // CPU clock. we consider it unsafe unless the user promises (via
        // command line) that it's patched and thus reliable on their system.
        bool usesTsc = IsSimilarMagnitude((double)m_frequency, os_cpu_ClockFrequency());
        // unconfirmed reports indicate QPC sometimes uses 1/3 of the
        // CPU clock frequency, so check that as well.
        usesTsc |= IsSimilarMagnitude((double)m_frequency, os_cpu_ClockFrequency()/3);
        if(usesTsc)
        {
            const bool isTscSafe = wutil_HasCommandLineArgument(L"-wQpcTscSafe");
            return isTscSafe;
        }

        // the HPET is reliable and used on Vista. it can't easily be recognized
        // since its frequency is variable (the spec says > 10 MHz; the master
        // 14.318 MHz oscillator is often used). considering frequencies in
        // [10, 100 MHz) to be a HPET would be dangerous because it may actually
        // be faster or RDTSC slower. we have to exclude all other cases and
        // assume it's a HPET - and thus safe - if we get here.
        return true;
    }

    u64 Counter() const
    {
        // fairly time-critical here, don't check the return value
        // (IsSupported made sure it succeeded initially)
        LARGE_INTEGER qpc_value;
        (void)QueryPerformanceCounter(&qpc_value);
        return qpc_value.QuadPart;
    }

    size_t CounterBits() const
    {
        // there are reports of incorrect rollover handling in the PMT
        // implementation of QPC (see CounterPMT::IsSafe). however, other
        // counters would be used on those systems, so it's irrelevant.
        // we'll report the full 64 bits.
        return 64;
    }

    double NominalFrequency() const
    {
        return (double)m_frequency;
    }

    double Resolution() const
    {
        return 1.0 / m_frequency;
    }

private:
    // used in several places and QPF is a bit slow+cumbersome.
    // (i64 allows easier conversion to double)
    i64 m_frequency;
};

ICounter* CreateCounterQPC(void* address, size_t size)
{
    ENSURE(sizeof(CounterQPC) <= size);
    return new(address) CounterQPC();
}