cregit-Linux how code gets into the kernel

Release 4.15 kernel/sched/cpupri.c

Directory: kernel/sched
 *  kernel/sched/cpupri.c
 *  CPU priority management
 *  Copyright (C) 2007-2008 Novell
 *  Author: Gregory Haskins <>
 *  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 <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/slab.h>
#include "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; }


Gregory Haskins56100.00%1100.00%

/** * 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. * * Return: (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); BUG_ON(task_pri >= CPUPRI_NR_PRIORITIES); 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; }


Gregory Haskins8252.56%225.00%
Steven Rostedt4931.41%337.50%
Rusty Russell1912.18%225.00%
Ingo Molnar63.85%112.50%

/** * cpupri_set - update the cpu priority setting * @cp: The cpupri context * @cpu: The target cpu * @newpri: 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(); 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(); /* * 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(); cpumask_clear_cpu(cpu, vec->mask); } *currpri = newpri; }


Gregory Haskins11868.60%116.67%
Steven Rostedt5029.07%350.00%
Peter Zijlstra31.74%116.67%
Yong Zhang10.58%116.67%

/** * cpupri_init - initialize the cpupri structure * @cp: The cpupri context * * Return: -ENOMEM on memory allocation failure. */
int cpupri_init(struct cpupri *cp) { int i; 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; } cp->cpu_to_pri = kcalloc(nr_cpu_ids, sizeof(int), GFP_KERNEL); if (!cp->cpu_to_pri) 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; }


Gregory Haskins5942.45%116.67%
Rusty Russell4935.25%116.67%
Peter Zijlstra2618.71%116.67%
Steven Rostedt32.16%116.67%
Pekka J Enberg10.72%116.67%
Yinghai Lu10.72%116.67%

/** * cpupri_cleanup - clean up the cpupri structure * @cp: The cpupri context */
void cpupri_cleanup(struct cpupri *cp) { int i; kfree(cp->cpu_to_pri); for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) free_cpumask_var(cp->pri_to_cpu[i].mask); }


Rusty Russell3782.22%133.33%
Peter Zijlstra715.56%133.33%
Gregory Haskins12.22%133.33%

Overall Contributors

Gregory Haskins31954.16%210.53%
Rusty Russell10618.00%210.53%
Steven Rostedt10217.32%421.05%
Peter Zijlstra416.96%315.79%
Ingo Molnar61.02%15.26%
Clark Williams61.02%15.26%
Tejun Heo30.51%15.26%
Yacine Belkadi20.34%15.26%
Randy Dunlap10.17%15.26%
Yinghai Lu10.17%15.26%
Pekka J Enberg10.17%15.26%
Yong Zhang10.17%15.26%
Directory: kernel/sched
Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.
Created with cregit.