+++ /dev/null
-/*
- * kernel/sched_cpupri.c
- *
- * CPU priority management
- *
- * Copyright (C) 2007-2008 Novell
- *
- * Author: Gregory Haskins <ghaskins@novell.com>
- *
- * 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), IDLE, NORMAL, RT1, ... RT99
- *
- * 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(102, nr_domcpus)), though the scenario that
- * yields the worst case search is fairly contrived.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; version 2
- * of the License.
- */
-
-#include <linux/gfp.h>
-#include "sched_cpupri.h"
-
-/* Convert between a 140 based task->prio, and our 102 based cpupri */
-static int convert_prio(int prio)
-{
- int cpupri;
-
- if (prio == CPUPRI_INVALID)
- cpupri = CPUPRI_INVALID;
- else if (prio == MAX_PRIO)
- cpupri = CPUPRI_IDLE;
- else if (prio >= MAX_RT_PRIO)
- cpupri = CPUPRI_NORMAL;
- else
- cpupri = MAX_RT_PRIO - prio + 1;
-
- return cpupri;
-}
-
-/**
- * cpupri_find - 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)
- *
- * 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.
- *
- * Returns: (int)bool - CPUs were found
- */
-int cpupri_find(struct cpupri *cp, struct task_struct *p,
- struct cpumask *lowest_mask)
-{
- int idx = 0;
- int task_pri = convert_prio(p->prio);
-
- if (task_pri >= MAX_RT_PRIO)
- return 0;
-
- for (idx = 0; idx < task_pri; idx++) {
- struct cpupri_vec *vec = &cp->pri_to_cpu[idx];
- int skip = 0;
-
- if (!atomic_read(&(vec)->count))
- skip = 1;
- /*
- * When looking at the vector, we need to read the counter,
- * do a memory barrier, then read the mask.
- *
- * Note: This is still all racey, but we can deal with it.
- * Ideally, we only want to look at masks that are set.
- *
- * If a mask is not set, then the only thing wrong is that we
- * did a little more work than necessary.
- *
- * If we read a zero count but the mask is set, because of the
- * memory barriers, that can only happen when the highest prio
- * task for a run queue has left the run queue, in which case,
- * it will be followed by a pull. If the task we are processing
- * fails to find a proper place to go, that pull request will
- * pull this task if the run queue is running at a lower
- * priority.
- */
- smp_rmb();
-
- /* Need to do the rmb for every iteration */
- if (skip)
- continue;
-
- if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
- continue;
-
- if (lowest_mask) {
- cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
-
- /*
- * We have to ensure that we have at least one bit
- * still set in the array, since the map could have
- * been concurrently emptied between the first and
- * second reads of vec->mask. If we hit this
- * condition, simply act as though we never hit this
- * priority level and continue on.
- */
- if (cpumask_any(lowest_mask) >= nr_cpu_ids)
- continue;
- }
-
- return 1;
- }
-
- return 0;
-}
-
-/**
- * cpupri_set - update the cpu priority setting
- * @cp: The cpupri context
- * @cpu: The target cpu
- * @pri: The priority (INVALID-RT99) 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)
-{
- int *currpri = &cp->cpu_to_pri[cpu];
- int oldpri = *currpri;
- int do_mb = 0;
-
- newpri = convert_prio(newpri);
-
- BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
-
- if (newpri == oldpri)
- return;
-
- /*
- * If the cpu was currently mapped to a different value, we
- * need to map it to the new value then remove the old value.
- * Note, we must add the new value first, otherwise we risk the
- * cpu being missed by the priority loop in cpupri_find.
- */
- if (likely(newpri != CPUPRI_INVALID)) {
- struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
-
- cpumask_set_cpu(cpu, vec->mask);
- /*
- * When adding a new vector, we update the mask first,
- * do a write memory barrier, and then update the count, to
- * make sure the vector is visible when count is set.
- */
- smp_mb__before_atomic_inc();
- atomic_inc(&(vec)->count);
- do_mb = 1;
- }
- if (likely(oldpri != CPUPRI_INVALID)) {
- struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri];
-
- /*
- * Because the order of modification of the vec->count
- * is important, we must make sure that the update
- * of the new prio is seen before we decrement the
- * old prio. This makes sure that the loop sees
- * one or the other when we raise the priority of
- * the run queue. We don't care about when we lower the
- * priority, as that will trigger an rt pull anyway.
- *
- * We only need to do a memory barrier if we updated
- * the new priority vec.
- */
- if (do_mb)
- smp_mb__after_atomic_inc();
-
- /*
- * When removing from the vector, we decrement the counter first
- * do a memory barrier and then clear the mask.
- */
- atomic_dec(&(vec)->count);
- smp_mb__after_atomic_inc();
- cpumask_clear_cpu(cpu, vec->mask);
- }
-
- *currpri = newpri;
-}
-
-/**
- * cpupri_init - initialize the cpupri structure
- * @cp: The cpupri context
- * @bootmem: true if allocations need to use bootmem
- *
- * Returns: -ENOMEM if memory fails.
- */
-int cpupri_init(struct cpupri *cp)
-{
- int i;
-
- memset(cp, 0, sizeof(*cp));
-
- for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
- struct cpupri_vec *vec = &cp->pri_to_cpu[i];
-
- atomic_set(&vec->count, 0);
- if (!zalloc_cpumask_var(&vec->mask, GFP_KERNEL))
- goto cleanup;
- }
-
- for_each_possible_cpu(i)
- cp->cpu_to_pri[i] = CPUPRI_INVALID;
- return 0;
-
-cleanup:
- for (i--; i >= 0; i--)
- free_cpumask_var(cp->pri_to_cpu[i].mask);
- return -ENOMEM;
-}
-
-/**
- * cpupri_cleanup - clean up the cpupri structure
- * @cp: The cpupri context
- */
-void cpupri_cleanup(struct cpupri *cp)
-{
- int i;
-
- for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
- free_cpumask_var(cp->pri_to_cpu[i].mask);
-}
projects / mirror_ubuntu-zesty-kernel.git / blobdiff