Create sched_rand() and move the LCG code into that. Call this when
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
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parent
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commit
0567b6cc16
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=279349
@ -302,6 +302,7 @@ static int sched_interact_score(struct thread *);
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static void sched_interact_update(struct thread *);
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static void sched_interact_fork(struct thread *);
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static void sched_pctcpu_update(struct td_sched *, int);
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static int sched_random(void);
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/* Operations on per processor queues */
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static struct thread *tdq_choose(struct tdq *);
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@ -356,6 +357,22 @@ SDT_PROBE_DEFINE(sched, , , remain__cpu);
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SDT_PROBE_DEFINE2(sched, , , surrender, "struct thread *",
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"struct proc *");
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/*
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* We need some randomness. Implement the classic Linear Congruential
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* generator X_{n+1}=(aX_n+c) mod m. These values are optimized for
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* m = 2^32, a = 69069 and c = 5. This is signed so that we can get
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* both positive and negative values from it by shifting the value
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* right.
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*/
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static int sched_random()
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{
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int rnd, *rndptr;
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rndptr = DPCPU_PTR(randomval);
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rnd = *rndptr * 69069 + 5;
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*rndptr = rnd;
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return(rnd);
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}
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/*
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* Print the threads waiting on a run-queue.
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*/
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@ -651,7 +668,7 @@ cpu_search(const struct cpu_group *cg, struct cpu_search *low,
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cpuset_t cpumask;
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struct cpu_group *child;
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struct tdq *tdq;
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int cpu, i, hload, lload, load, total, rnd, *rndptr;
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int cpu, i, hload, lload, load, total, rnd;
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total = 0;
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cpumask = cg->cg_mask;
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@ -700,8 +717,7 @@ cpu_search(const struct cpu_group *cg, struct cpu_search *low,
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CPU_CLR(cpu, &cpumask);
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tdq = TDQ_CPU(cpu);
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load = tdq->tdq_load * 256;
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rndptr = DPCPU_PTR(randomval);
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rnd = (*rndptr = *rndptr * 69069 + 5) >> 26;
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rnd = sched_random() >> 26; /* -32 to +31 */
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if (match & CPU_SEARCH_LOWEST) {
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if (cpu == low->cs_prefer)
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load -= 64;
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@ -861,14 +877,11 @@ sched_balance(void)
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{
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struct tdq *tdq;
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/*
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* Select a random time between .5 * balance_interval and
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* 1.5 * balance_interval.
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*/
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balance_ticks = max(balance_interval / 2, 1);
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balance_ticks += random() % balance_interval;
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if (smp_started == 0 || rebalance == 0)
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return;
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balance_ticks = max(balance_interval / 2, 1) +
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((sched_random() >> 16) % balance_interval);
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tdq = TDQ_SELF();
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TDQ_UNLOCK(tdq);
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sched_balance_group(cpu_top);
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