linux/kernel/sched/cpupri.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  kernel/sched/cpupri.c
 *
 *  CPU priority management
 *
 *  Copyright (C) 2007-2008 Novell
 *
 *  Author: Gregory Haskins <[email protected]>
 *
 *  This code tracks the priority of each CPU so that global migration
 *  decisions are easy to calculate.  Each CPU can be in a state as follows:
 *
 *                 (INVALID), NORMAL, RT1, ... RT99, HIGHER
 *
 *  going from the lowest priority to the highest.  CPUs in the INVALID state
 *  are not eligible for routing.  The system maintains this state with
 *  a 2 dimensional bitmap (the first for priority class, the second for CPUs
 *  in that class).  Therefore a typical application without affinity
 *  restrictions can find a suitable CPU with O(1) complexity (e.g. two bit
 *  searches).  For tasks with affinity restrictions, the algorithm has a
 *  worst case complexity of O(min(101, nr_domcpus)), though the scenario that
 *  yields the worst case search is fairly contrived.
 */

/*
 * p->rt_priority   p->prio   newpri   cpupri
 *
 *				  -1       -1 (CPUPRI_INVALID)
 *
 *				  99        0 (CPUPRI_NORMAL)
 *
 *		1        98       98        1
 *	      ...
 *	       49        50       50       49
 *	       50        49       49       50
 *	      ...
 *	       99         0        0       99
 *
 *				 100	  100 (CPUPRI_HIGHER)
 */
static int convert_prio(int prio)
{ … }

static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p,
				struct cpumask *lowest_mask, int idx)
{ … }

int cpupri_find(struct cpupri *cp, struct task_struct *p,
		struct cpumask *lowest_mask)
{ … }

/**
 * cpupri_find_fitness - find the best (lowest-pri) CPU in the system
 * @cp: The cpupri context
 * @p: The task
 * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
 * @fitness_fn: A pointer to a function to do custom checks whether the CPU
 *              fits a specific criteria so that we only return those CPUs.
 *
 * Note: This function returns the recommended CPUs as calculated during the
 * current invocation.  By the time the call returns, the CPUs may have in
 * fact changed priorities any number of times.  While not ideal, it is not
 * an issue of correctness since the normal rebalancer logic will correct
 * any discrepancies created by racing against the uncertainty of the current
 * priority configuration.
 *
 * Return: (int)bool - CPUs were found
 */
int cpupri_find_fitness(struct cpupri *cp, struct task_struct *p,
		struct cpumask *lowest_mask,
		bool (*fitness_fn)(struct task_struct *p, int cpu))
{ … }

/**
 * cpupri_set - update the CPU priority setting
 * @cp: The cpupri context
 * @cpu: The target CPU
 * @newpri: The priority (INVALID,NORMAL,RT1-RT99,HIGHER) to assign to this CPU
 *
 * Note: Assumes cpu_rq(cpu)->lock is locked
 *
 * Returns: (void)
 */
void cpupri_set(struct cpupri *cp, int cpu, int newpri)
{ … }

/**
 * cpupri_init - initialize the cpupri structure
 * @cp: The cpupri context
 *
 * Return: -ENOMEM on memory allocation failure.
 */
int cpupri_init(struct cpupri *cp)
{ … }

/**
 * cpupri_cleanup - clean up the cpupri structure
 * @cp: The cpupri context
 */
void cpupri_cleanup(struct cpupri *cp)
{ … }