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Create sched_rand() and move the LCG code into that. Call this when

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we need randomness in ULE. This removes random() call from the
rebalance interval code.

Submitted by: Harrison Grundy
Differential Revision: https://reviews.freebsd.org/D1968
This commit is contained in:
Warner Losh 2015-02-27 02:56:58 +00:00
parent 999efd901b
commit 0567b6cc16
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=279349
1 changed files with 22 additions and 9 deletions
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31
sys/kern/sched_ule.c
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@ -302,6 +302,7 @@ static int sched_interact_score(struct thread *);
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 *);
@ -356,6 +357,22 @@ SDT_PROBE_DEFINE(sched, , , remain__cpu);
SDT_PROBE_DEFINE2(sched, , , surrender, "struct thread *",
"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 * 69069 + 5;
*rndptr = rnd;
return(rnd);
}
/*
* Print the threads waiting on a run-queue.
*/
@ -651,7 +668,7 @@ cpu_search(const struct cpu_group *cg, struct cpu_search *low,
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;
@ -700,8 +717,7 @@ cpu_search(const struct cpu_group *cg, struct cpu_search *low,
CPU_CLR(cpu, &cpumask);
tdq = TDQ_CPU(cpu);
load = tdq->tdq_load * 256;
rndptr = DPCPU_PTR(randomval);
rnd = (*rndptr = *rndptr * 69069 + 5) >> 26;
rnd = sched_random() >> 26; /* -32 to +31 */
if (match & CPU_SEARCH_LOWEST) {
if (cpu == low->cs_prefer)
load -= 64;
@ -861,14 +877,11 @@ sched_balance(void)
{
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);