arch/x86/kernel/itmt.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * itmt.c: Support Intel Turbo Boost Max Technology 3.0
 *
 * (C) Copyright 2016 Intel Corporation
 * Author: Tim Chen <tim.c.chen@linux.intel.com>
 *
 * On platforms supporting Intel Turbo Boost Max Technology 3.0, (ITMT),
 * the maximum turbo frequencies of some cores in a CPU package may be
 * higher than for the other cores in the same package.  In that case,
 * better performance can be achieved by making the scheduler prefer
 * to run tasks on the CPUs with higher max turbo frequencies.
 *
 * This file provides functions and data structures for enabling the
 * scheduler to favor scheduling on cores can be boosted to a higher
 * frequency under ITMT.
 */

#include <linux/sched.h>
#include <linux/cpumask.h>
#include <linux/cpuset.h>
#include <linux/debugfs.h>
#include <linux/mutex.h>
#include <linux/sysctl.h>
#include <linux/nodemask.h>

static DEFINE_MUTEX(itmt_update_mutex);
DEFINE_PER_CPU_READ_MOSTLY(int, sched_core_priority);

/* Boolean to track if system has ITMT capabilities */
static bool __read_mostly sched_itmt_capable;

/*
 * Boolean to control whether we want to move processes to cpu capable
 * of higher turbo frequency for cpus supporting Intel Turbo Boost Max
 * Technology 3.0.
 *
 * It can be set via /sys/kernel/debug/x86/sched_itmt_enabled
 */
bool __read_mostly sysctl_sched_itmt_enabled;

static ssize_t sched_itmt_enabled_write(struct file *filp,
					const char __user *ubuf,
					size_t cnt, loff_t *ppos)
{
	ssize_t result;
	bool orig;

	guard(mutex)(&itmt_update_mutex);

	orig = sysctl_sched_itmt_enabled;
	result = debugfs_write_file_bool(filp, ubuf, cnt, ppos);

	if (sysctl_sched_itmt_enabled != orig) {
		x86_topology_update = true;
		rebuild_sched_domains();
	}

	return result;
}

static int sched_core_priority_show(struct seq_file *s, void *unused)
{
	int cpu;

	seq_puts(s, "CPU #\tPriority\n");
	for_each_possible_cpu(cpu)
		seq_printf(s, "%d\t%d\n", cpu, arch_asym_cpu_priority(cpu));

	return 0;
}
DEFINE_SHOW_ATTRIBUTE(sched_core_priority);

static const struct file_operations dfs_sched_itmt_fops = {
	.read =         debugfs_read_file_bool,
	.write =        sched_itmt_enabled_write,
	.open =         simple_open,
	.llseek =       default_llseek,
};

static struct dentry *dfs_sched_itmt;
static struct dentry *dfs_sched_core_prio;

/**
 * sched_set_itmt_support() - Indicate platform supports ITMT
 *
 * This function is used by the OS to indicate to scheduler that the platform
 * is capable of supporting the ITMT feature.
 *
 * The current scheme has the pstate driver detects if the system
 * is ITMT capable and call sched_set_itmt_support.
 *
 * This must be done only after sched_set_itmt_core_prio
 * has been called to set the cpus' priorities.
 * It must not be called with cpu hot plug lock
 * held as we need to acquire the lock to rebuild sched domains
 * later.
 *
 * Return: 0 on success
 */
int sched_set_itmt_support(void)
{
	guard(mutex)(&itmt_update_mutex);

	if (sched_itmt_capable)
		return 0;

	dfs_sched_itmt = debugfs_create_file_unsafe("sched_itmt_enabled",
						    0644,
						    arch_debugfs_dir,
						    &sysctl_sched_itmt_enabled,
						    &dfs_sched_itmt_fops);
	if (IS_ERR(dfs_sched_itmt))
		dfs_sched_itmt = NULL;

	dfs_sched_core_prio = debugfs_create_file("sched_core_priority", 0644,
						  arch_debugfs_dir, NULL,
						  &sched_core_priority_fops);
	if (IS_ERR(dfs_sched_core_prio))
		dfs_sched_core_prio = NULL;

	sched_itmt_capable = true;

	sysctl_sched_itmt_enabled = 1;

	x86_topology_update = true;
	rebuild_sched_domains();

	return 0;
}

/**
 * sched_clear_itmt_support() - Revoke platform's support of ITMT
 *
 * This function is used by the OS to indicate that it has
 * revoked the platform's support of ITMT feature.
 *
 * It must not be called with cpu hot plug lock
 * held as we need to acquire the lock to rebuild sched domains
 * later.
 */
void sched_clear_itmt_support(void)
{
	guard(mutex)(&itmt_update_mutex);

	if (!sched_itmt_capable)
		return;

	sched_itmt_capable = false;

	debugfs_remove(dfs_sched_itmt);
	dfs_sched_itmt = NULL;
	debugfs_remove(dfs_sched_core_prio);
	dfs_sched_core_prio = NULL;

	if (sysctl_sched_itmt_enabled) {
		/* disable sched_itmt if we are no longer ITMT capable */
		sysctl_sched_itmt_enabled = 0;
		x86_topology_update = true;
		rebuild_sched_domains();
	}
}

int arch_asym_cpu_priority(int cpu)
{
	return per_cpu(sched_core_priority, cpu);
}

/**
 * sched_set_itmt_core_prio() - Set CPU priority based on ITMT
 * @prio:	Priority of @cpu
 * @cpu:	The CPU number
 *
 * The pstate driver will find out the max boost frequency
 * and call this function to set a priority proportional
 * to the max boost frequency. CPUs with higher boost
 * frequency will receive higher priority.
 *
 * No need to rebuild sched domain after updating
 * the CPU priorities. The sched domains have no
 * dependency on CPU priorities.
 */
void sched_set_itmt_core_prio(int prio, int cpu)
{
	per_cpu(sched_core_priority, cpu) = prio;
}