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![Thomas Gleixner](/assets/img/avatar_default.png)
Use the future-safe accessor for struct task_struct's. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/r/1462969411-17735-1-git-send-email-bigeasy@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
248 lines
6.8 KiB
C
248 lines
6.8 KiB
C
/*
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* kernel/sched/cpupri.c
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*
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* CPU priority management
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*
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* Copyright (C) 2007-2008 Novell
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*
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* Author: Gregory Haskins <ghaskins@novell.com>
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*
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* This code tracks the priority of each CPU so that global migration
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* decisions are easy to calculate. Each CPU can be in a state as follows:
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*
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* (INVALID), IDLE, NORMAL, RT1, ... RT99
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*
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* going from the lowest priority to the highest. CPUs in the INVALID state
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* are not eligible for routing. The system maintains this state with
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* a 2 dimensional bitmap (the first for priority class, the second for cpus
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* in that class). Therefore a typical application without affinity
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* restrictions can find a suitable CPU with O(1) complexity (e.g. two bit
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* searches). For tasks with affinity restrictions, the algorithm has a
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* worst case complexity of O(min(102, nr_domcpus)), though the scenario that
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* yields the worst case search is fairly contrived.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; version 2
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* of the License.
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*/
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#include <linux/gfp.h>
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#include <linux/sched.h>
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#include <linux/sched/rt.h>
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#include <linux/slab.h>
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#include "cpupri.h"
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/* Convert between a 140 based task->prio, and our 102 based cpupri */
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static int convert_prio(int prio)
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{
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int cpupri;
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if (prio == CPUPRI_INVALID)
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cpupri = CPUPRI_INVALID;
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else if (prio == MAX_PRIO)
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cpupri = CPUPRI_IDLE;
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else if (prio >= MAX_RT_PRIO)
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cpupri = CPUPRI_NORMAL;
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else
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cpupri = MAX_RT_PRIO - prio + 1;
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return cpupri;
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}
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/**
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* cpupri_find - find the best (lowest-pri) CPU in the system
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* @cp: The cpupri context
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* @p: The task
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* @lowest_mask: A mask to fill in with selected CPUs (or NULL)
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*
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* Note: This function returns the recommended CPUs as calculated during the
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* current invocation. By the time the call returns, the CPUs may have in
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* fact changed priorities any number of times. While not ideal, it is not
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* an issue of correctness since the normal rebalancer logic will correct
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* any discrepancies created by racing against the uncertainty of the current
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* priority configuration.
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*
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* Return: (int)bool - CPUs were found
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*/
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int cpupri_find(struct cpupri *cp, struct task_struct *p,
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struct cpumask *lowest_mask)
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{
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int idx = 0;
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int task_pri = convert_prio(p->prio);
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BUG_ON(task_pri >= CPUPRI_NR_PRIORITIES);
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for (idx = 0; idx < task_pri; idx++) {
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struct cpupri_vec *vec = &cp->pri_to_cpu[idx];
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int skip = 0;
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if (!atomic_read(&(vec)->count))
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skip = 1;
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/*
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* When looking at the vector, we need to read the counter,
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* do a memory barrier, then read the mask.
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*
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* Note: This is still all racey, but we can deal with it.
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* Ideally, we only want to look at masks that are set.
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*
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* If a mask is not set, then the only thing wrong is that we
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* did a little more work than necessary.
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*
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* If we read a zero count but the mask is set, because of the
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* memory barriers, that can only happen when the highest prio
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* task for a run queue has left the run queue, in which case,
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* it will be followed by a pull. If the task we are processing
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* fails to find a proper place to go, that pull request will
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* pull this task if the run queue is running at a lower
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* priority.
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*/
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smp_rmb();
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/* Need to do the rmb for every iteration */
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if (skip)
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continue;
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if (cpumask_any_and(tsk_cpus_allowed(p), vec->mask) >= nr_cpu_ids)
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continue;
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if (lowest_mask) {
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cpumask_and(lowest_mask, tsk_cpus_allowed(p), vec->mask);
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/*
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* We have to ensure that we have at least one bit
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* still set in the array, since the map could have
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* been concurrently emptied between the first and
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* second reads of vec->mask. If we hit this
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* condition, simply act as though we never hit this
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* priority level and continue on.
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*/
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if (cpumask_any(lowest_mask) >= nr_cpu_ids)
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continue;
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}
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return 1;
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}
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return 0;
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}
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/**
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* cpupri_set - update the cpu priority setting
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* @cp: The cpupri context
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* @cpu: The target cpu
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* @newpri: The priority (INVALID-RT99) to assign to this CPU
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*
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* Note: Assumes cpu_rq(cpu)->lock is locked
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*
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* Returns: (void)
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*/
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void cpupri_set(struct cpupri *cp, int cpu, int newpri)
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{
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int *currpri = &cp->cpu_to_pri[cpu];
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int oldpri = *currpri;
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int do_mb = 0;
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newpri = convert_prio(newpri);
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BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
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if (newpri == oldpri)
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return;
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/*
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* If the cpu was currently mapped to a different value, we
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* need to map it to the new value then remove the old value.
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* Note, we must add the new value first, otherwise we risk the
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* cpu being missed by the priority loop in cpupri_find.
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*/
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if (likely(newpri != CPUPRI_INVALID)) {
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struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
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cpumask_set_cpu(cpu, vec->mask);
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/*
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* When adding a new vector, we update the mask first,
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* do a write memory barrier, and then update the count, to
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* make sure the vector is visible when count is set.
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*/
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smp_mb__before_atomic();
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atomic_inc(&(vec)->count);
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do_mb = 1;
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}
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if (likely(oldpri != CPUPRI_INVALID)) {
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struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri];
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/*
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* Because the order of modification of the vec->count
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* is important, we must make sure that the update
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* of the new prio is seen before we decrement the
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* old prio. This makes sure that the loop sees
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* one or the other when we raise the priority of
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* the run queue. We don't care about when we lower the
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* priority, as that will trigger an rt pull anyway.
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*
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* We only need to do a memory barrier if we updated
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* the new priority vec.
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*/
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if (do_mb)
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smp_mb__after_atomic();
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/*
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* When removing from the vector, we decrement the counter first
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* do a memory barrier and then clear the mask.
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*/
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atomic_dec(&(vec)->count);
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smp_mb__after_atomic();
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cpumask_clear_cpu(cpu, vec->mask);
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}
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*currpri = newpri;
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}
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/**
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* cpupri_init - initialize the cpupri structure
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* @cp: The cpupri context
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*
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* Return: -ENOMEM on memory allocation failure.
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*/
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int cpupri_init(struct cpupri *cp)
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{
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int i;
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memset(cp, 0, sizeof(*cp));
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for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
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struct cpupri_vec *vec = &cp->pri_to_cpu[i];
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atomic_set(&vec->count, 0);
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if (!zalloc_cpumask_var(&vec->mask, GFP_KERNEL))
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goto cleanup;
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}
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cp->cpu_to_pri = kcalloc(nr_cpu_ids, sizeof(int), GFP_KERNEL);
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if (!cp->cpu_to_pri)
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goto cleanup;
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for_each_possible_cpu(i)
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cp->cpu_to_pri[i] = CPUPRI_INVALID;
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return 0;
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cleanup:
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for (i--; i >= 0; i--)
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free_cpumask_var(cp->pri_to_cpu[i].mask);
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return -ENOMEM;
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}
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/**
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* cpupri_cleanup - clean up the cpupri structure
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* @cp: The cpupri context
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*/
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void cpupri_cleanup(struct cpupri *cp)
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{
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int i;
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kfree(cp->cpu_to_pri);
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for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
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free_cpumask_var(cp->pri_to_cpu[i].mask);
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}
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