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/*
* Copyright (c) 2021 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.
*
* Copyright (c) 2006 The Regents of The University of Michigan
* Copyright (c) 2013 Advanced Micro Devices, Inc.
* Copyright (c) 2013 Mark D. Hill and David A. Wood
* All rights reserved.
*
* 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.
*/
#include "sim/simulate.hh"
#include <atomic>
#include <mutex>
#include <thread>
#include "base/logging.hh"
#include "base/pollevent.hh"
#include "base/types.hh"
#include "sim/async.hh"
#include "sim/eventq.hh"
#include "sim/sim_events.hh"
#include "sim/sim_exit.hh"
#include "sim/stat_control.hh"
namespace gem5
{
//! forward declaration
Event *doSimLoop(EventQueue *);
GlobalSimLoopExitEvent *simulate_limit_event = nullptr;
class SimulatorThreads
{
public:
SimulatorThreads() = delete;
SimulatorThreads(const SimulatorThreads &) = delete;
SimulatorThreads &operator=(SimulatorThreads &) = delete;
SimulatorThreads(uint32_t num_queues)
: terminate(false),
numQueues(num_queues),
barrier(num_queues)
{
threads.reserve(num_queues);
}
~SimulatorThreads()
{
// This should only happen after exit has been
// called. Subordinate event queues should normally (assuming
// exit is called from Python) be waiting on the barrier when
// this happens.
//
// N.B.: Not terminating here would make it impossible to
// safely destroy the barrier.
terminateThreads();
}
void runUntilLocalExit()
{
assert(!terminate);
// Start subordinate threads if needed.
if (threads.empty()) {
// the main thread (the one running Python) handles queue 0,
// so we only need to allocate new threads for queues 1..N-1.
// We'll call these the "subordinate" threads.
for (uint32_t i = 1; i < numQueues; i++) {
threads.emplace_back(
[this](EventQueue *eq) {
thread_main(eq);
}, mainEventQueue[i]);
}
}
// This method is called from the main thread. All subordinate
// threads should be waiting on the barrier when the function
// is called. The arrival of the main thread here will satisfy
// the barrier and start another iteration in the thread loop.
barrier.wait();
}
void
terminateThreads()
{
assert(!terminate);
if (threads.empty())
return;
/* This function should only be called when the simulator is
* handling a global exit event (typically from Python). This
* means that the helper threads will be waiting on the
* barrier. Tell the helper threads to exit and release them from
* their barrier. */
terminate = true;
barrier.wait();
/* Wait for all of the threads to terminate */
for (auto &t : threads) {
t.join();
}
terminate = false;
threads.clear();
}
protected:
/**
* The main function for all subordinate threads (i.e., all threads
* other than the main thread). These threads start by waiting on
* threadBarrier. Once all threads have arrived at threadBarrier,
* they enter the simulation loop concurrently. When they exit the
* loop, they return to waiting on threadBarrier. This process is
* repeated until the simulation terminates.
*/
void
thread_main(EventQueue *queue)
{
/* Wait for all initialisation to complete */
barrier.wait();
while (!terminate) {
doSimLoop(queue);
barrier.wait();
}
}
std::atomic<bool> terminate;
uint32_t numQueues;
std::vector<std::thread> threads;
Barrier barrier;
};
static std::unique_ptr<SimulatorThreads> simulatorThreads;
struct DescheduleDeleter
{
void operator()(BaseGlobalEvent *event)
{
if (!event)
return;
event->deschedule();
delete event;
}
};
/** Simulate for num_cycles additional cycles. If num_cycles is -1
* (the default), do not limit simulation; some other event must
* terminate the loop. Exported to Python.
* @return The SimLoopExitEvent that caused the loop to exit.
*/
GlobalSimLoopExitEvent *
simulate(Tick num_cycles)
{
std::unique_ptr<GlobalSyncEvent, DescheduleDeleter> quantum_event;
const Tick exit_tick = num_cycles < MaxTick - curTick() ?
curTick() + num_cycles : MaxTick;
inform("Entering event queue @ %d. Starting simulation...\n", curTick());
if (!simulatorThreads)
simulatorThreads.reset(new SimulatorThreads(numMainEventQueues));
if (!simulate_limit_event) {
simulate_limit_event = new GlobalSimLoopExitEvent(
mainEventQueue[0]->getCurTick(),
"simulate() limit reached", 0);
}
simulate_limit_event->reschedule(exit_tick);
if (numMainEventQueues > 1) {
fatal_if(simQuantum == 0,
"Quantum for multi-eventq simulation not specified");
quantum_event.reset(
new GlobalSyncEvent(curTick() + simQuantum, simQuantum,
EventBase::Progress_Event_Pri, 0));
inParallelMode = true;
}
simulatorThreads->runUntilLocalExit();
Event *local_event = doSimLoop(mainEventQueue[0]);
assert(local_event);
inParallelMode = false;
// locate the global exit event and return it to Python
BaseGlobalEvent *global_event = local_event->globalEvent();
assert(global_event);
GlobalSimLoopExitEvent *global_exit_event =
dynamic_cast<GlobalSimLoopExitEvent *>(global_event);
assert(global_exit_event);
return global_exit_event;
}
void
terminateEventQueueThreads()
{
simulatorThreads->terminateThreads();
}
/**
* Test and clear the global async_event flag, such that each time the
* flag is cleared, only one thread returns true (and thus is assigned
* to handle the corresponding async event(s)).
*/
static bool
testAndClearAsyncEvent()
{
static std::mutex mutex;
bool was_set = false;
mutex.lock();
if (async_event) {
was_set = true;
async_event = false;
}
mutex.unlock();
return was_set;
}
/**
* The main per-thread simulation loop. This loop is executed by all
* simulation threads (the main thread and the subordinate threads) in
* parallel.
*/
Event *
doSimLoop(EventQueue *eventq)
{
// set the per thread current eventq pointer
curEventQueue(eventq);
eventq->handleAsyncInsertions();
while (1) {
// there should always be at least one event (the SimLoopExitEvent
// we just scheduled) in the queue
assert(!eventq->empty());
assert(curTick() <= eventq->nextTick() &&
"event scheduled in the past");
if (async_event && testAndClearAsyncEvent()) {
// Take the event queue lock in case any of the service
// routines want to schedule new events.
std::lock_guard<EventQueue> lock(*eventq);
if (async_statdump || async_statreset) {
statistics::schedStatEvent(async_statdump, async_statreset);
async_statdump = false;
async_statreset = false;
}
if (async_io) {
async_io = false;
pollQueue.service();
}
if (async_exit) {
async_exit = false;
exitSimLoop("user interrupt received");
}
if (async_exception) {
async_exception = false;
return NULL;
}
}
Event *exit_event = eventq->serviceOne();
if (exit_event != NULL) {
return exit_event;
}
}
// not reached... only exit is return on SimLoopExitEvent
}
} // namespace gem5