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![Gregory Haskins](/assets/img/avatar_default.png)
The current code use a linear algorithm which causes scaling issues on larger SMP machines. This patch replaces that algorithm with a 2-dimensional bitmap to reduce latencies in the wake-up path. Signed-off-by: Gregory Haskins <ghaskins@novell.com> Acked-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
174 lines
4.4 KiB
C
174 lines
4.4 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 "sched_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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#define for_each_cpupri_active(array, idx) \
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for (idx = find_first_bit(array, CPUPRI_NR_PRIORITIES); \
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idx < CPUPRI_NR_PRIORITIES; \
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idx = find_next_bit(array, CPUPRI_NR_PRIORITIES, idx+1))
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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
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*
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* Note: This function returns the recommended CPUs as calculated during the
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* current invokation. 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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* Returns: (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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cpumask_t *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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for_each_cpupri_active(cp->pri_active, idx) {
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struct cpupri_vec *vec = &cp->pri_to_cpu[idx];
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cpumask_t mask;
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if (idx >= task_pri)
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break;
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cpus_and(mask, p->cpus_allowed, vec->mask);
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if (cpus_empty(mask))
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continue;
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*lowest_mask = mask;
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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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* @pri: 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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unsigned long flags;
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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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* first need to unmap the old value
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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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spin_lock_irqsave(&vec->lock, flags);
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vec->count--;
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if (!vec->count)
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clear_bit(oldpri, cp->pri_active);
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cpu_clear(cpu, vec->mask);
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spin_unlock_irqrestore(&vec->lock, flags);
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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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spin_lock_irqsave(&vec->lock, flags);
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cpu_set(cpu, vec->mask);
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vec->count++;
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if (vec->count == 1)
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set_bit(newpri, cp->pri_active);
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spin_unlock_irqrestore(&vec->lock, flags);
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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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* Returns: (void)
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*/
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void 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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spin_lock_init(&vec->lock);
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vec->count = 0;
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cpus_clear(vec->mask);
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}
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for_each_possible_cpu(i)
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cp->cpu_to_pri[i] = CPUPRI_INVALID;
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}
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