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D1981.id4018.diff
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D1981.id4018.diff

Index: sys/kern/sched_ule.c
===================================================================
--- sys/kern/sched_ule.c
+++ sys/kern/sched_ule.c
@@ -360,17 +360,18 @@
/*
* 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.
+ * m = 2^32, a = 69069 and c = 5. We only return the upper 16 bits
+ * of the random state (in the low bits of our answer) to return
+ * the maximum randomness.
*/
-static int sched_random()
+static uint32_t sched_random()
{
- int rnd, *rndptr;
- rndptr = DPCPU_PTR(randomval);
- rnd = *rndptr * 69069 + 5;
- *rndptr = rnd;
- return(rnd);
+ uint32_t *rndptr;
+
+ rndptr = DPCPU_PTR(randomval);
+ *rndptr = *rndptr * 69069 + 5;
+
+ return (*rndptr >> 16);
}
#endif
@@ -718,7 +719,7 @@
CPU_CLR(cpu, &cpumask);
tdq = TDQ_CPU(cpu);
load = tdq->tdq_load * 256;
- rnd = sched_random() >> 26; /* -32 to +31 */
+ rnd = sched_random() & 31;
if (match & CPU_SEARCH_LOWEST) {
if (cpu == low->cs_prefer)
load -= 64;
@@ -882,7 +883,7 @@
return;
balance_ticks = max(balance_interval / 2, 1) +
- ((sched_random() >> 16) % balance_interval);
+ (sched_random() % balance_interval);
tdq = TDQ_SELF();
TDQ_UNLOCK(tdq);
sched_balance_group(cpu_top);

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