u/linux: Add helpers to raise thread scheduling priority

src/xrt/auxiliary/util/CMakeLists.txt

@@ -117,6 +117,11 @@ if(WIN32)
 	target_sources(aux_util PRIVATE u_windows.c u_windows.h)
 endif()
 
+# Only uses POSIX/Linux libraries, doesn't add anything extra.
+if(XRT_HAVE_LINUX OR ANDROID)
+	target_sources(aux_util PRIVATE u_linux.c u_linux.h)
+endif()
+
 # Is basically used everywhere, unavoidable.
 if(XRT_HAVE_SYSTEM_CJSON)
 	target_link_libraries(aux_util PUBLIC cJSON::cJSON)

src/xrt/auxiliary/util/u_linux.c

@@ -0,0 +1,139 @@
+// Copyright 2023, Collabora, Ltd.
+// SPDX-License-Identifier: BSL-1.0
+/*!
+ * @file
+ * @brief  Various helpers for doing Linux specific things.
+ * @author Jakob Bornecrantz <jakob@collabora.com>
+ *
+ * @ingroup aux_util
+ */
+
+#include "util/u_linux.h"
+#include "util/u_pretty_print.h"
+
+#include <pthread.h>
+#include <assert.h>
+#include <unistd.h>
+#include <sched.h>
+#include <stdio.h>
+
+#define LOG_D(...) U_LOG_IFL_D(log_level, __VA_ARGS__)
+#define LOG_I(...) U_LOG_IFL_I(log_level, __VA_ARGS__)
+#define LOG_W(...) U_LOG_IFL_W(log_level, __VA_ARGS__)
+#define LOG_E(...) U_LOG_IFL_E(log_level, __VA_ARGS__)
+
+#define NAME_LENGTH 32
+
+
+/*
+ *
+ * Helper functions.
+ *
+ */
+
+static const char *
+policy_to_string(int policy)
+{
+	switch (policy) {
+	case SCHED_FIFO: return "SCHED_FIFO";
+	case SCHED_RR: return "SCHED_RR";
+	case SCHED_OTHER: return "SCHED_OTHER(normal)";
+	case SCHED_IDLE: return "SCHED_IDLE";
+	case SCHED_BATCH: return "SCHED_BATCH";
+	default: return "SCHED_<UNKNOWN>";
+	}
+}
+
+static void
+get_name(char *str, size_t count)
+{
+	assert(str != NULL);
+	assert(count > 0);
+
+	// First init.
+	str[0] = '\0';
+
+	// Get name of thread.
+	pthread_t this_thread = pthread_self();
+	pthread_getname_np(this_thread, str, count);
+
+	if (str[0] == '\0') {
+		snprintf(str, count, "tid(%i)", gettid());
+	}
+}
+
+static void
+print_thread_info(struct u_pp_delegate dg, enum u_logging_level log_level, pthread_t thread)
+{
+	struct sched_param params;
+	int policy = 0;
+	int ret = 0;
+
+	// Get the policy and scheduling priority.
+	ret = pthread_getschedparam(thread, &policy, &params);
+	if (ret != 0) {
+		LOG_E("pthread_getschedparam: %i", ret);
+		return;
+	}
+
+	u_pp(dg, "policy: '%s', priority: '%i'", policy_to_string(policy), params.sched_priority);
+}
+
+
+/*
+ *
+ * 'Exported' functions.
+ *
+ */
+
+void
+u_linux_try_to_set_realtime_priority_on_thread(enum u_logging_level log_level, const char *name)
+{
+	pthread_t this_thread = pthread_self();
+	struct u_pp_sink_stack_only sink;
+	struct sched_param params;
+	char str[NAME_LENGTH];
+	int ret;
+
+	// Add printing delegate.
+	struct u_pp_delegate dg = u_pp_sink_stack_only_init(&sink);
+
+	// Always have some name.
+	if (name == NULL) {
+		get_name(str, ARRAY_SIZE(str));
+		name = str;
+	}
+
+	if (log_level <= U_LOGGING_DEBUG) {
+		u_pp(dg, "Trying to raise priority on thread '%s'\n\t", name);
+		u_pp(dg, "before: ");
+		print_thread_info(dg, log_level, this_thread);
+	}
+
+	// Get the maximum on this platform.
+	params.sched_priority = sched_get_priority_max(SCHED_FIFO);
+
+	// Here we try to set the realtime scheduling with the max priority available.
+	ret = pthread_setschedparam(this_thread, SCHED_FIFO, &params);
+
+	// Print different amount depending on log level.
+	if (log_level <= U_LOGGING_DEBUG) {
+		u_pp(dg, "after: ");
+		print_thread_info(dg, log_level, this_thread);
+		u_pp(dg, "\n\tResult: %i", ret);
+	} else {
+		if (ret != 0) {
+			u_pp(dg, "Could not raise priority for thread '%s'", name);
+		} else {
+			u_pp(dg, "Raised priority of thread '%s' to ", name);
+			print_thread_info(dg, log_level, this_thread);
+		}
+	}
+
+	// Always print as warning or information.
+	if (ret != 0) {
+		LOG_W("%s", sink.buffer);
+	} else {
+		LOG_I("%s", sink.buffer);
+	}
+}

src/xrt/auxiliary/util/u_linux.h

@@ -0,0 +1,39 @@
+// Copyright 2023, Collabora, Ltd.
+// SPDX-License-Identifier: BSL-1.0
+/*!
+ * @file
+ * @brief  Various helpers for doing Linux specific things.
+ * @author Jakob Bornecrantz <jakob@collabora.com>
+ *
+ * @ingroup aux_util
+ */
+
+#pragma once
+
+#include "xrt/xrt_compiler.h"
+#include "xrt/xrt_windows.h"
+#include "util/u_logging.h"
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/*!
+ * Try to set realtime priority on this thread. Passing in log_level to control
+ * how chatty this function is, the name is to make the logging pretty, can be
+ * NULL and the code will try to figure out the name itself.
+ *
+ * @param name      Thread name to be used in logging.
+ * @param log_level Logging level to control chattiness.
+ *
+ * @aux_util
+ */
+void
+u_linux_try_to_set_realtime_priority_on_thread(enum u_logging_level log_level, const char *name);
+
+
+#ifdef __cplusplus
+}
+#endif