blender/intern/cycles/util/util_task.cpp

/*
 * Copyright 2011-2013 Blender Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "util/util_foreach.h"
#include "util/util_logging.h"
#include "util/util_system.h"
#include "util/util_task.h"
#include "util/util_time.h"

//#define THREADING_DEBUG_ENABLED

#ifdef THREADING_DEBUG_ENABLED
#include <stdio.h>
#define THREADING_DEBUG(...) do { printf(__VA_ARGS__); fflush(stdout); } while(0)
#else
#define THREADING_DEBUG(...)
#endif

CCL_NAMESPACE_BEGIN

/* Task Pool */

TaskPool::TaskPool()
{
	num_tasks_handled = 0;
	num = 0;
	do_cancel = false;
}

TaskPool::~TaskPool()
{
	stop();
}

void TaskPool::push(Task *task, bool front)
{
	TaskScheduler::Entry entry;

	entry.task = task;
	entry.pool = this;

	TaskScheduler::push(entry, front);
}

void TaskPool::push(const TaskRunFunction& run, bool front)
{
	push(new Task(run), front);
}

void TaskPool::wait_work(Summary *stats)
{
	thread_scoped_lock num_lock(num_mutex);

	while(num != 0) {
		num_lock.unlock();

		thread_scoped_lock queue_lock(TaskScheduler::queue_mutex);

		/* find task from this pool. if we get a task from another pool,
		 * we can get into deadlock */
		TaskScheduler::Entry work_entry;
		bool found_entry = false;
		list<TaskScheduler::Entry>::iterator it;

		for(it = TaskScheduler::queue.begin(); it != TaskScheduler::queue.end(); it++) {
			TaskScheduler::Entry& entry = *it;

			if(entry.pool == this) {
				work_entry = entry;
				found_entry = true;
				TaskScheduler::queue.erase(it);
				break;
			}
		}

		queue_lock.unlock();

		/* if found task, do it, otherwise wait until other tasks are done */
		if(found_entry) {
			/* run task */
			work_entry.task->run(0);

			/* delete task */
			delete work_entry.task;

			/* notify pool task was done */
			num_decrease(1);
		}

		num_lock.lock();
		if(num == 0)
			break;

		if(!found_entry) {
			THREADING_DEBUG("num==%d, Waiting for condition in TaskPool::wait_work !found_entry\n", num);
			num_cond.wait(num_lock);
			THREADING_DEBUG("num==%d, condition wait done in TaskPool::wait_work !found_entry\n", num);
		}
	}

	if(stats != NULL) {
		stats->time_total = time_dt() - start_time;
		stats->num_tasks_handled = num_tasks_handled;
	}
}

void TaskPool::cancel()
{
	do_cancel = true;

	TaskScheduler::clear(this);

	{
		thread_scoped_lock num_lock(num_mutex);

		while(num) {
			THREADING_DEBUG("num==%d, Waiting for condition in TaskPool::cancel\n", num);
			num_cond.wait(num_lock);
			THREADING_DEBUG("num==%d condition wait done in TaskPool::cancel\n", num);
		}
	}

	do_cancel = false;
}

void TaskPool::stop()
{
	TaskScheduler::clear(this);

	assert(num == 0);
}

bool TaskPool::canceled()
{
	return do_cancel;
}

bool TaskPool::finished()
{
	thread_scoped_lock num_lock(num_mutex);
	return num == 0;
}

void TaskPool::num_decrease(int done)
{
	num_mutex.lock();
	num -= done;

	assert(num >= 0);
	if(num == 0) {
		THREADING_DEBUG("num==%d, notifying all in TaskPool::num_decrease\n", num);
		num_cond.notify_all();
	}

	num_mutex.unlock();
}

void TaskPool::num_increase()
{
	thread_scoped_lock num_lock(num_mutex);
	if(num_tasks_handled == 0) {
		start_time = time_dt();
	}
	num++;
	num_tasks_handled++;
	THREADING_DEBUG("num==%d, notifying all in TaskPool::num_increase\n", num);
	num_cond.notify_all();
}

/* Task Scheduler */

thread_mutex TaskScheduler::mutex;
int TaskScheduler::users = 0;
vector<thread*> TaskScheduler::threads;
bool TaskScheduler::do_exit = false;

list<TaskScheduler::Entry> TaskScheduler::queue;
thread_mutex TaskScheduler::queue_mutex;
thread_condition_variable TaskScheduler::queue_cond;

namespace {

/* Get number of processors on each of the available nodes. The result is sized
 * by the highest node index, and element corresponds to number of processors on
 * that node.
 * If node is not available, then the corresponding number of processors is
 * zero. */
void get_per_node_num_processors(vector<int>* num_per_node_processors)
{
	const int num_nodes = system_cpu_num_numa_nodes();
	if(num_nodes == 0) {
		LOG(ERROR) << "Zero available NUMA nodes, is not supposed to happen.";
		return;
	}
	num_per_node_processors->resize(num_nodes);
	for(int node = 0; node < num_nodes; ++node) {
		if(!system_cpu_is_numa_node_available(node)) {
			(*num_per_node_processors)[node] = 0;
			continue;
		}
		(*num_per_node_processors)[node] =
		        system_cpu_num_numa_node_processors(node);
	}
}

/* Calculate total number of processors on all available nodes.
 * This is similar to system_cpu_thread_count(), but uses pre-calculated number
 * of processors on each of the node, avoiding extra system calls and checks for
 * the node availability. */
int get_num_total_processors(const vector<int>& num_per_node_processors)
{
	int num_total_processors = 0;
	foreach(int num_node_processors, num_per_node_processors) {
		num_total_processors += num_node_processors;
	}
	return num_total_processors;
}

/* Compute NUMA node for every thread to run on, for the best performance. */
vector<int> distribute_threads_on_nodes(const int num_threads)
{
	/* Start with all threads unassigned to any specific NUMA node. */
	vector<int> thread_nodes(num_threads, -1);
	const int num_active_group_processors =
	        system_cpu_num_active_group_processors();
	VLOG(1) << "Detected " << num_active_group_processors << " processors "
	        << "in active group.";
	if(num_active_group_processors >= num_threads) {
		/* If the current thread is set up in a way that its affinity allows to
		 * use at least requested number of threads we do not explicitly set
		 * affinity to the worker therads.
		 * This way we allow users to manually edit affinity of the parent
		 * thread, and here we follow that affinity. This way it's possible to
		 * have two Cycles/Blender instances running manually set to a different
		 * dies on a CPU. */
		VLOG(1) << "Not setting thread group affinity.";
		return thread_nodes;
	}
	vector<int> num_per_node_processors;
	get_per_node_num_processors(&num_per_node_processors);
	if(num_per_node_processors.size() == 0) {
		/* Error was already repported, here we can't do anything, so we simply
		 * leave default affinity to all the worker threads. */
		return thread_nodes;
	}
	const int num_nodes = num_per_node_processors.size();
	int thread_index = 0;
	/* First pass: fill in all the nodes to their maximum.
	*
	 * If there is less threads than the overall nodes capacity, some of the
	 * nodes or parts of them will idle.
	 *
	 * TODO(sergey): Consider picking up fastest nodes if number of threads
	 * fits on them. For example, on Threadripper2 we might consider using nodes
	 * 0 and 2 if user requested 32 render threads. */
	const int num_total_node_processors =
	        get_num_total_processors(num_per_node_processors);
	int current_node_index = 0;
	while(thread_index < num_total_node_processors &&
	      thread_index < num_threads) {
		const int num_node_processors =
		        num_per_node_processors[current_node_index];
		for(int processor_index = 0;
		    processor_index < num_node_processors;
		    ++processor_index)
		{
			VLOG(1) << "Scheduling thread " << thread_index << " to node "
			        << current_node_index << ".";
			thread_nodes[thread_index] = current_node_index;
			++thread_index;
			if(thread_index == num_threads) {
				/* All threads are scheduled on their nodes. */
				return thread_nodes;
			}
		}
		++current_node_index;
	}
	/* Second pass: keep scheduling threads to each node one by one, uniformly
	 * fillign them in.
	 * This is where things becomes tricky to predict for the maximum
	 * performance: on the one hand this avoids too much threading overhead on
	 * few nodes, but for the final performance having all the overhead on one
	 * node might be better idea (since other nodes will have better chance of
	 * rendering faster).
	 * But more tricky is that nodes might have difference capacity, so we might
	 * want to do some weighted scheduling. For example, if node 0 has 16
	 * processors and node 1 has 32 processors, we'd better schedule 1 extra
	 * thread on node 0 and 2 extra threads on node 1. */
	current_node_index = 0;
	while(thread_index < num_threads) {
		/* Skip unavailable nodes. */
		/* TODO(sergey): Add sanity check against deadlock. */
		while(num_per_node_processors[current_node_index] == 0) {
			current_node_index = (current_node_index + 1) % num_nodes;
		}
		VLOG(1) << "Scheduling thread " << thread_index << " to node "
		        << current_node_index << ".";
		++thread_index;
		current_node_index = (current_node_index + 1) % num_nodes;
	}

	return thread_nodes;
}

}  // namespace

void TaskScheduler::init(int num_threads)
{
	thread_scoped_lock lock(mutex);
	/* Multiple cycles instances can use this task scheduler, sharing the same
	 * threads, so we keep track of the number of users. */
	++users;
	if(users != 1) {
		return;
	}
	do_exit = false;
	const bool use_auto_threads = (num_threads == 0);
	if(use_auto_threads) {
		/* Automatic number of threads. */
		num_threads = system_cpu_thread_count();
	}
	VLOG(1) << "Creating pool of " << num_threads << " threads.";

	/* Compute distribution on NUMA nodes. */
	vector<int> thread_nodes = distribute_threads_on_nodes(num_threads);

	/* Launch threads that will be waiting for work. */
	threads.resize(num_threads);
	for(int thread_index = 0; thread_index < num_threads; ++thread_index) {
		threads[thread_index] = new thread(
		        function_bind(&TaskScheduler::thread_run, thread_index + 1),
		        thread_nodes[thread_index]);
	}
}

void TaskScheduler::exit()
{
	thread_scoped_lock lock(mutex);
	users--;
	if(users == 0) {
		VLOG(1) << "De-initializing thread pool of task scheduler.";
		/* stop all waiting threads */
		TaskScheduler::queue_mutex.lock();
		do_exit = true;
		TaskScheduler::queue_cond.notify_all();
		TaskScheduler::queue_mutex.unlock();

		/* delete threads */
		foreach(thread *t, threads) {
			t->join();
			delete t;
		}
		threads.clear();
	}
}

void TaskScheduler::free_memory()
{
	assert(users == 0);
	threads.free_memory();
}

bool TaskScheduler::thread_wait_pop(Entry& entry)
{
	thread_scoped_lock queue_lock(queue_mutex);

	while(queue.empty() && !do_exit)
		queue_cond.wait(queue_lock);

	if(queue.empty()) {
		assert(do_exit);
		return false;
	}

	entry = queue.front();
	queue.pop_front();

	return true;
}

void TaskScheduler::thread_run(int thread_id)
{
	Entry entry;

	/* todo: test affinity/denormal mask */

	/* keep popping off tasks */
	while(thread_wait_pop(entry)) {
		/* run task */
		entry.task->run(thread_id);

		/* delete task */
		delete entry.task;

		/* notify pool task was done */
		entry.pool->num_decrease(1);
	}
}

void TaskScheduler::push(Entry& entry, bool front)
{
	entry.pool->num_increase();

	/* add entry to queue */
	TaskScheduler::queue_mutex.lock();
	if(front)
		TaskScheduler::queue.push_front(entry);
	else
		TaskScheduler::queue.push_back(entry);

	TaskScheduler::queue_cond.notify_one();
	TaskScheduler::queue_mutex.unlock();
}

void TaskScheduler::clear(TaskPool *pool)
{
	thread_scoped_lock queue_lock(TaskScheduler::queue_mutex);

	/* erase all tasks from this pool from the queue */
	list<Entry>::iterator it = queue.begin();
	int done = 0;

	while(it != queue.end()) {
		Entry& entry = *it;

		if(entry.pool == pool) {
			done++;
			delete entry.task;

			it = queue.erase(it);
		}
		else
			it++;
	}

	queue_lock.unlock();

	/* notify done */
	pool->num_decrease(done);
}

/* Dedicated Task Pool */

DedicatedTaskPool::DedicatedTaskPool()
{
	do_cancel = false;
	do_exit = false;
	num = 0;

	worker_thread = new thread(function_bind(&DedicatedTaskPool::thread_run, this));
}

DedicatedTaskPool::~DedicatedTaskPool()
{
	stop();
	worker_thread->join();
	delete worker_thread;
}

void DedicatedTaskPool::push(Task *task, bool front)
{
	num_increase();

	/* add task to queue */
	queue_mutex.lock();
	if(front)
		queue.push_front(task);
	else
		queue.push_back(task);

	queue_cond.notify_one();
	queue_mutex.unlock();
}

void DedicatedTaskPool::push(const TaskRunFunction& run, bool front)
{
	push(new Task(run), front);
}

void DedicatedTaskPool::wait()
{
	thread_scoped_lock num_lock(num_mutex);

	while(num)
		num_cond.wait(num_lock);
}

void DedicatedTaskPool::cancel()
{
	do_cancel = true;

	clear();
	wait();

	do_cancel = false;
}

void DedicatedTaskPool::stop()
{
	clear();

	do_exit = true;
	queue_cond.notify_all();

	wait();

	assert(num == 0);
}

bool DedicatedTaskPool::canceled()
{
	return do_cancel;
}

void DedicatedTaskPool::num_decrease(int done)
{
	thread_scoped_lock num_lock(num_mutex);
	num -= done;

	assert(num >= 0);
	if(num == 0)
		num_cond.notify_all();
}

void DedicatedTaskPool::num_increase()
{
	thread_scoped_lock num_lock(num_mutex);
	num++;
	num_cond.notify_all();
}

bool DedicatedTaskPool::thread_wait_pop(Task*& task)
{
	thread_scoped_lock queue_lock(queue_mutex);

	while(queue.empty() && !do_exit)
		queue_cond.wait(queue_lock);

	if(queue.empty()) {
		assert(do_exit);
		return false;
	}

	task = queue.front();
	queue.pop_front();

	return true;
}

void DedicatedTaskPool::thread_run()
{
	Task *task;

	/* keep popping off tasks */
	while(thread_wait_pop(task)) {
		/* run task */
		task->run(0);

		/* delete task */
		delete task;

		/* notify task was done */
		num_decrease(1);
	}
}

void DedicatedTaskPool::clear()
{
	thread_scoped_lock queue_lock(queue_mutex);

	/* erase all tasks from the queue */
	list<Task*>::iterator it = queue.begin();
	int done = 0;

	while(it != queue.end()) {
		done++;
		delete *it;

		it = queue.erase(it);
	}

	queue_lock.unlock();

	/* notify done */
	num_decrease(done);
}

string TaskPool::Summary::full_report() const
{
	string report = "";
	report += string_printf("Total time:    %f\n", time_total);
	report += string_printf("Tasks handled: %d\n", num_tasks_handled);
	return report;
}

CCL_NAMESPACE_END