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sched: adaptive scheduler granularity

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Instead of specifying the preemption granularity, specify the wanted
latency. By fixing the granlarity to a constany the wakeup latency
it a function of the number of running tasks on the rq.

Invert this relation.

sysctl_sched_granularity becomes a minimum for the dynamic granularity
computed from the new sysctl_sched_latency.

Then use this latency to do more intelligent granularity decisions: if
there are fewer tasks running then we can schedule coarser. This helps
performance while still always keeping the latency target.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
2007-08-25 18:41:53 +02:00
committed by Ingo Molnar
parent 1fc84aaae3
commit 218050855e
4 changed files with 86 additions and 17 deletions
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14
kernel/sched.c
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@@ -4911,14 +4911,18 @@ cpumask_t nohz_cpu_mask = CPU_MASK_NONE;
static inline void sched_init_granularity(void)
{
unsigned int factor = 1 + ilog2(num_online_cpus());
const unsigned long gran_limit = 100000000;
const unsigned long limit = 100000000;
sysctl_sched_granularity *= factor;
if (sysctl_sched_granularity > gran_limit)
sysctl_sched_granularity = gran_limit;
if (sysctl_sched_granularity > limit)
sysctl_sched_granularity = limit;
sysctl_sched_runtime_limit = sysctl_sched_granularity * 5;
sysctl_sched_wakeup_granularity = sysctl_sched_granularity / 2;
sysctl_sched_latency *= factor;
if (sysctl_sched_latency > limit)
sysctl_sched_latency = limit;
sysctl_sched_runtime_limit = sysctl_sched_latency * 5;
sysctl_sched_wakeup_granularity = sysctl_sched_latency / 2;
}
#ifdef CONFIG_SMP