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/*
* Copyright (c) 2012 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef __CPU_KVM_TIMER_HH__
#define __CPU_KVM_TIMER_HH__
#include <ctime>
#include "cpu/kvm/perfevent.hh"
#include "sim/core.hh"
/**
* Timer functions to interrupt VM execution after a number of
* simulation ticks. The timer allows scaling of the host time to take
* performance differences between the simulated and real CPU into
* account.
*
* The performance scaling factor is ratio between the target's CPI
* and the host's CPI. It is larger than 1 if the host is faster than
* the target and lower than 1 if it is slower.
*
* When the timer times out, it sends a signal to the thread that
* started the timer. The signal forces KVM to drop out of the system
* call that started the guest and hands control to gem5.
*/
class BaseKvmTimer
{
public:
/**
* Setup basic timer functionality shared by all timer
* implementations.
*
* @param signo Signal to deliver
* @param hostFactor Performance scaling factor
* @param hostFreq Clock frequency of the host
*/
BaseKvmTimer(int signo, float hostFactor, Tick hostFreq)
: signo(signo), _resolution(0),
hostFactor(hostFactor), hostFreq(hostFreq) {};
virtual ~BaseKvmTimer() {};
/**
* Arm the timer so that it fires after a certain number of ticks.
*
* @note A timer implementation is free to convert between
* simulation ticks and virtualized time using any method it
* chooses. The accuracy of the timer therefore depends on what it
* measures, an accurate timer implementation should measure the
* number of cycles or instructions executed in the guest. If such
* counters are unavailable, it may fallback to wall clock time.
*
* @param ticks Number of ticks until the timer fires
*/
virtual void arm(Tick ticks) = 0;
/**
* Disarm the timer.
*
* When this method has returned, the timer may no longer deliver
* signals upon timeout.
*/
virtual void disarm() = 0;
virtual bool expired() {
return true;
}
/**
* Determine the resolution of the timer in ticks. This method is
* mainly used to determine the smallest number of ticks the timer
* can wait before triggering a signal.
*
* @return Minimum number of ticks the timer can resolve
*/
Tick resolution() {
if (_resolution == 0)
_resolution = calcResolution();
return _resolution;
}
/**
* Convert cycles executed on the host into Ticks executed in the
* simulator. Scales the results using the hostFactor to take CPU
* performance differences into account.
*
* @return Host cycles executed in VM converted to simulation ticks
*/
Tick ticksFromHostCycles(uint64_t cycles) {
return cycles * hostFactor * hostFreq;
}
/**
* Convert nanoseconds executed on the host into Ticks executed in
* the simulator. Scales the results using the hostFactor to take
* CPU performance differences into account.
*
* @return Nanoseconds executed in VM converted to simulation ticks
*/
Tick ticksFromHostNs(uint64_t ns) {
return ns * hostFactor * SimClock::Float::ns;
}
protected:
/**
* Calculate the timer resolution, used by resolution() which
* caches the result.
*
* @return Minimum number of ticks the timer can resolve
*/
virtual Tick calcResolution() = 0;
/**
* Convert a time in simulator ticks to host nanoseconds.
*
* @return Simulation ticks converted into nanoseconds on the host
*/
uint64_t hostNs(Tick ticks) {
return ticks / (SimClock::Float::ns * hostFactor);
}
/**
* Convert a time in simulator ticks to host cycles
*
*
* @return Simulation ticks converted into CPU cycles on the host
*/
uint64_t hostCycles(Tick ticks) {
return ticks / (hostFreq * hostFactor);
}
/** Signal to deliver when the timer times out */
int signo;
private:
/** Cached resolution */
mutable Tick _resolution;
/** Performance scaling factor */
float hostFactor;
/** Host frequency */
Tick hostFreq;
};
/**
* Timer based on standard POSIX timers. The POSIX timer API supports
* several different clock with different characteristics.
*
* @note It might be tempting to use
* CLOCK_(THREAD|PROCESS)_CPUTIME_ID, however, this clock usually has
* much lower resolution than the real-time clocks.
*/
class PosixKvmTimer : public BaseKvmTimer
{
public:
/**
* @param signo Signal to deliver
* @param clockID ID of the clock to use
* @param hostFactor Performance scaling factor
* @param hostFreq Clock frequency of the host
*/
PosixKvmTimer(int signo, clockid_t clockID,
float hostFactor, Tick hostFreq);
~PosixKvmTimer();
void arm(Tick ticks) override;
void disarm() override;
bool expired() override;
protected:
Tick calcResolution() override;
private:
clockid_t clockID;
timer_t timer;
struct itimerspec prevTimerSpec;
};
/**
* PerfEvent based timer using the host's CPU cycle counter.
*
* @warning There is a known problem in some versions of the PerfEvent
* API that prevents the counter overflow period from being updated
* reliably, which might break this timer. See PerfKvmCounter::period()
* for details.
*/
class PerfKvmTimer : public BaseKvmTimer
{
public:
/**
* Create a timer that uses an existing hardware cycle counter.
*
* @note The performance counter must be configured for overflow
* sampling, which in practice means that it must have a non-zero
* sample period. The initial sample period is ignored since
* period will be updated when arm() is called.
*
* @param ctr Attached performance counter configured for overflow
* reporting.
* @param signo Signal to deliver
* @param hostFactor Performance scaling factor
* @param hostFreq Clock frequency of the host
*/
PerfKvmTimer(PerfKvmCounter &ctr,
int signo,
float hostFactor, Tick hostFreq);
~PerfKvmTimer();
void arm(Tick ticks);
void disarm();
protected:
Tick calcResolution();
private:
PerfKvmCounter &hwOverflow;
};
#endif