power_state.cc

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#include "sim/power_state.hh"
 
#include <cassert>
 
#include "base/logging.hh"
#include "base/trace.hh"
#include "debug/PowerDomain.hh"
#include "sim/cur_tick.hh"
#include "sim/power_domain.hh"
#include "sim/serialize.hh"
 
namespace gem5
{
 
PowerState::PowerState(const PowerStateParams &p) :
    SimObject(p), _currState(p.default_state),
    possibleStates(p.possible_states.begin(),
                   p.possible_states.end()),
    stats(*this)
{
    for (auto &pm: p.leaders) {
        // Register this object as a follower. This object is
        // dependent on pm for power state transitions
        pm->addFollower(this);
    }
}
 
void
PowerState::setControlledDomain(PowerDomain* pwr_dom)
{
    // Only a power domain can register as dependant of a power stated
    // object
    controlledDomain = pwr_dom;
    DPRINTF(PowerDomain, "%s is registered as controlled by %s \n",
                         pwr_dom->name(), name());
}
 
void
PowerState::serialize(CheckpointOut &cp) const
{
    unsigned int currState = (unsigned int)_currState;
 
    SERIALIZE_SCALAR(currState);
    SERIALIZE_SCALAR(prvEvalTick);
}
 
void
PowerState::unserialize(CheckpointIn &cp)
{
    unsigned int currState;
 
    UNSERIALIZE_SCALAR(currState);
    UNSERIALIZE_SCALAR(prvEvalTick);
 
    _currState = enums::PwrState(currState);
}
 
void
PowerState::set(enums::PwrState p)
{
    // Check if this power state is actually allowed by checking whether it is
    // present in pwrStateToIndex-dictionary
    panic_if(possibleStates.find(p) == possibleStates.end(),
             "Cannot go to %s in %s \n", enums::PwrStateStrings[p], name());
 
    // Function should ideally be called only when there is a state change
    if (_currState == p) {
        warn_once("PowerState: Already in the requested power state, "
                  "request ignored");
        return;
    }
 
    // No need to compute stats if in the same tick, update state though. This
    // can happen in cases like a) during start of the simulation multiple
    // state changes happens in init/startup phase, b) one takes a decision to
    // migrate state but decides to reverts back to the original state in the
    // same tick if other conditions are not met elsewhere.
    // Any state change related stats would have been recorded on previous call
    // to this function.
    if (prvEvalTick == curTick() && curTick() != 0) {
        warn("PowerState: More than one power state change request "
             "encountered within the same simulation tick");
        _currState = p;
        return;
    }
 
    // Record stats for previous state.
    computeStats();
 
    _currState = p;
 
    stats.numTransitions++;
 
    // Update the domain this object controls, if there is one
    if (controlledDomain) {
        controlledDomain->pwrStateChangeCallback(p, this);
    }
 
}
 
enums::PwrState
PowerState::matchPwrState(enums::PwrState p)
{
    // If the object is asked to match a power state, it has to be a follower
    // and hence should not have a pointer to a powerDomain
    assert(controlledDomain == nullptr);
 
    // If we are already in this power state, ignore request
    if (_currState == p) {
        DPRINTF(PowerDomain, "Already in p-state %s requested to match \n",
                enums::PwrStateStrings[p]);
        return _currState;
    }
 
    enums::PwrState old_state = _currState;
    if (possibleStates.find(p) != possibleStates.end()) {
        // If this power state is allowed in this object, just go there
        set(p);
    } else {
        // Loop over all power states in this object and find a power state
        // which is more performant than the requested one (considering we
        // cannot match it exactly)
        for (auto rev_it = possibleStates.crbegin();
             rev_it != possibleStates.crend(); rev_it++) {
            if (*(rev_it) <= p) {
                // This power state is the least performant power state that is
                // still more performant than the requested one
                DPRINTF(PowerDomain, "Best match for %s is %s \n",
                        enums::PwrStateStrings[p],
                        enums::PwrStateStrings[*(rev_it)]);
                set(*(rev_it));
                break;
            }
        }
    }
    // Check if the transition happened
    // The only case in which the power state cannot change is if the
    // object is already at in its most performant state.
    warn_if((_currState == old_state) &&
            possibleStates.find(_currState) != possibleStates.begin(),
            "Transition to power state %s was not possible, SimObject already"
            " in the most performance state %s",
            enums::PwrStateStrings[p], enums::PwrStateStrings[_currState]);
 
    stats.numPwrMatchStateTransitions++;
    return _currState;
}
 
void
PowerState::computeStats()
{
    // Calculate time elapsed from last (valid) state change
    Tick elapsed_time = curTick() - prvEvalTick;
 
    stats.pwrStateResidencyTicks[_currState] += elapsed_time;
 
    // Time spent in CLK_GATED state, this might change depending on
    // transition to other low power states in respective simulation
    // objects.
    if (_currState == enums::PwrState::CLK_GATED) {
        stats.ticksClkGated.sample(elapsed_time);
    }
 
    prvEvalTick = curTick();
}
 
std::vector<double>
PowerState::getWeights() const
{
    // Get residency stats
    std::vector<double> ret;
    statistics::VCounter residencies;
    stats.pwrStateResidencyTicks.value(residencies);
 
    // Account for current state too!
    Tick elapsed_time = curTick() - prvEvalTick;
    residencies[_currState] += elapsed_time;
 
    ret.resize(enums::PwrState::Num_PwrState);
    for (unsigned i = 0; i < enums::PwrState::Num_PwrState; i++)
        ret[i] = residencies[i] / \
                     (stats.pwrStateResidencyTicks.total() + elapsed_time);
 
    return ret;
}
 
PowerState::PowerStateStats::PowerStateStats(PowerState &co)
    : statistics::Group(&co),
    powerState(co),
    ADD_STAT(numTransitions, statistics::units::Count::get(),
             "Number of power state transitions"),
    ADD_STAT(numPwrMatchStateTransitions, statistics::units::Count::get(),
             "Number of power state transitions due match request"),
    ADD_STAT(ticksClkGated, statistics::units::Tick::get(),
             "Distribution of time spent in the clock gated state"),
    ADD_STAT(pwrStateResidencyTicks, statistics::units::Tick::get(),
             "Cumulative time (in ticks) in various power states")
{
}
 
void
PowerState::PowerStateStats::regStats()
{
    statistics::Group::regStats();
 
    using namespace statistics;
 
    const PowerStateParams &p = powerState.params();
 
    numTransitions.flags(nozero);
    numPwrMatchStateTransitions.flags(nozero);
 
    // Each sample is time in ticks
    unsigned num_bins = std::max(p.clk_gate_bins, 10U);
    ticksClkGated
        .init(p.clk_gate_min, p.clk_gate_max,
            (p.clk_gate_max - p.clk_gate_min + 1.0) / num_bins)
        .flags(pdf | nozero | nonan)
        ;
 
    pwrStateResidencyTicks
        .init(enums::PwrState::Num_PwrState)
        .flags(nozero)
        ;
    for (int i = 0; i < enums::PwrState::Num_PwrState; i++) {
        pwrStateResidencyTicks.subname(i, enums::PwrStateStrings[i]);
    }
 
    numTransitions = 0;
}
 
void
PowerState::PowerStateStats::preDumpStats()
{
    statistics::Group::preDumpStats();
 
    powerState.computeStats();
}
 
} // namespace gem5