VILLASnode/common/lib/kernel/rt.cpp

/* Linux specific real-time optimizations.
 *
 * Author: Steffen Vogel <post@steffenvogel.de>
 * SPDX-FileCopyrightText: 2014-2023 Institute for Automation of Complex Power Systems, RWTH Aachen University
 * SPDX-License-Identifier: Apache-2.0
 */

#include <sched.h>
#include <unistd.h>

#include <villas/log.hpp>
#include <villas/cpuset.hpp>
#include <villas/config.hpp>
#include <villas/utils.hpp>
#include <villas/exceptions.hpp>

#include <villas/kernel/kernel.hpp>
#include <villas/kernel/kernel.hpp>
#include <villas/kernel/rt.hpp>

#ifdef __linux__
  using villas::utils::CpuSet;
#endif // __linux__

namespace villas {
namespace kernel {
namespace rt {

void init(int priority, int affinity)
{
	Logger logger = logging.get("kernel:rt");

	logger->info("Initialize sub-system");

#ifdef __linux__
	int is_rt, is_isol;
	char isolcpus[255];

	// Use FIFO scheduler with real time priority
	is_rt = isPreemptible();
	if (!is_rt)
		logger->warn("We recommend to use an PREEMPT_RT patched kernel!");

	if (priority)
		setPriority(priority);
	else
		logger->warn("You might want to use the 'priority' setting to increase " PROJECT_NAME "'s process priority");

	if (affinity) {
		is_isol = getCmdlineParam("isolcpus", isolcpus, sizeof(isolcpus));
		if (is_isol)
			logger->warn("You should reserve some cores for " PROJECT_NAME " (see 'isolcpus')");
		else {
			CpuSet cset_pin(affinity);
			CpuSet cset_isol(isolcpus);
			CpuSet cset_non_isol = ~cset_isol & cset_pin;

			if (cset_non_isol.count() > 0)
				logger->warn("Affinity setting includes cores which are not isolated: affinity={}, isolcpus={}, non_isolated={}", (std::string) cset_pin, (std::string) cset_isol, (std::string) cset_non_isol);
		}

		setProcessAffinity(affinity);
	}
	else
		logger->warn("You might want to use the 'affinity' setting to pin " PROJECT_NAME " to dedicate CPU cores");
#else
	logger->warn("This platform is not optimized for real-time execution");

	(void) affinity;
	(void) priority;
#endif // __linux__
}

#ifdef __linux__
void setProcessAffinity(int affinity)
{
	int ret;

	assert(affinity != 0);

	Logger logger = logging.get("kernel:rt");

	// Pin threads to CPUs by setting the affinity
	CpuSet cset_pin(affinity);

	ret = sched_setaffinity(0, cset_pin.size(), cset_pin);
	if (ret)
		throw SystemError("Failed to set CPU affinity of process");

	logger->debug("Set affinity to {} {}", cset_pin.count() == 1 ? "core" : "cores", (std::string) cset_pin);
}

void setThreadAffinity(pthread_t thread, int affinity)
{
	int ret;

	assert(affinity != 0);

	Logger logger = logging.get("kernel:rt");

	CpuSet cset_pin(affinity);

	ret = pthread_setaffinity_np(thread, cset_pin.size(), cset_pin);
	if (ret)
		throw SystemError("Failed to set CPU affinity of thread");

	logger->debug("Set affinity of thread {} to {} {}", (long unsigned) thread, cset_pin.count() == 1 ? "core" : "cores", (std::string) cset_pin);
}

void setPriority(int priority)
{
	int ret;
	struct sched_param param;
	param.sched_priority = priority;

	Logger logger = logging.get("kernel:rt");

	ret = sched_setscheduler(0, SCHED_FIFO, &param);
	if (ret)
		throw SystemError("Failed to set real time priority");

	logger->debug("Task priority set to {}", priority);
}

bool isPreemptible()
{
	return access(SYSFS_PATH "/kernel/realtime", R_OK) == 0;
}

#endif // __linux__

} // namespace villas
} // namespace kernel
} // namespace rt