1 files changed, 241 insertions, 0 deletions

diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c
new file mode 100644
index 000000000000..b0d798eaf130
--- /dev/null
+++ b/kernel/sched/cpupri.c
@@ -0,0 +1,241 @@
+/*
+ *  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 "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);
+}