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Index: sys/kern/sched_ule.c
===================================================================
--- sys/kern/sched_ule.c
+++ sys/kern/sched_ule.c
@@ -302,6 +302,7 @@
static void sched_interact_update(struct thread *);
static void sched_interact_fork(struct thread *);
static void sched_pctcpu_update(struct td_sched *, int);
+static int sched_random(void);
/* Operations on per processor queues */
static struct thread *tdq_choose(struct tdq *);
@@ -357,6 +358,21 @@
"struct proc *");
/*
+ * We need some randomness. Implement the classic Linear Congruential
+ * generator X_{n+1}=(aX_n+c) mod m. These values are optimized for
+ * m = 2^32, a = 69069 and c = 5. This is signed so that we can get
+ * both positive and negative values from it by shifting the value
+ * right.
+ */
+static int sched_random()
+{
+ int rnd, *rndptr;
+ rndptr = DPCPU_PTR(randomval);
+ rnd = (*rndptr = *rndptr * 69069 + 5);
+ return(rnd);
+}
+
+/*
* Print the threads waiting on a run-queue.
*/
static void
@@ -651,7 +667,7 @@
cpuset_t cpumask;
struct cpu_group *child;
struct tdq *tdq;
- int cpu, i, hload, lload, load, total, rnd, *rndptr;
+ int cpu, i, hload, lload, load, total, rnd;
total = 0;
cpumask = cg->cg_mask;
@@ -700,9 +716,8 @@
CPU_CLR(cpu, &cpumask);
tdq = TDQ_CPU(cpu);
load = tdq->tdq_load * 256;
- rndptr = DPCPU_PTR(randomval);
- rnd = (*rndptr = *rndptr * 69069 + 5) >> 26;
- if (match & CPU_SEARCH_LOWEST) {
+ rnd = sched_random() >> 26; /* -32 to +31 */
+ if (match & CPU_SEARCH_LOWEST) {
if (cpu == low->cs_prefer)
load -= 64;
/* If that CPU is allowed and get data. */
@@ -861,14 +876,11 @@
{
struct tdq *tdq;
- /*
- * Select a random time between .5 * balance_interval and
- * 1.5 * balance_interval.
- */
- balance_ticks = max(balance_interval / 2, 1);
- balance_ticks += random() % balance_interval;
if (smp_started == 0 || rebalance == 0)
return;
+
+ balance_ticks = max(balance_interval / 2, 1) +
+ ((sched_random() >> 16) % balance_interval);
tdq = TDQ_SELF();
TDQ_UNLOCK(tdq);
sched_balance_group(cpu_top);

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