mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 19:00:25 +00:00
![Yacine Belkadi](/assets/img/avatar_default.png)
When building the htmldocs (in verbose mode), scripts/kernel-doc reports the follwing type of warnings: Warning(kernel/sched/core.c:936): No description found for return value of 'task_curr' ... Fix those by: - adding the missing descriptions - using "Return" sections for the descriptions Signed-off-by: Yacine Belkadi <yacine.belkadi.1@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1373654747-2389-1-git-send-email-yacine.belkadi.1@gmail.com [ While at it, fix the cpupri_set() explanation. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
242 lines
6.7 KiB
C
242 lines
6.7 KiB
C
/*
|
|
* 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 <linux/sched.h>
|
|
#include <linux/sched/rt.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;
|
|
}
|
|
|
|
/**
|
|
* 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);
|
|
|
|
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
|
|
* @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_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
|
|
*
|
|
* Return: -ENOMEM on memory allocation failure.
|
|
*/
|
|
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);
|
|
}
|