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sched: reintroduce SMP tunings again

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Yanmin Zhang reported an aim7 regression and bisected it down to:

 |  commit 38ad464d41
 |  Author: Ingo Molnar <mingo@elte.hu>
 |  Date:   Mon Oct 15 17:00:02 2007 +0200
 |
 |     sched: uniform tunings
 |
 |     use the same defaults on both UP and SMP.

fix this by reintroducing similar SMP tunings again. This resolves
the regression.

(also update the comments to match the ilog2(nr_cpus) tuning effect)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar 2007-11-09 22:39:38 +01:00
parent fa13a5a1f2
commit 19978ca610
2 changed files with 37 additions and 9 deletions
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28
kernel/sched.c
View file

@ -4992,6 +4992,32 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
*/
cpumask_t nohz_cpu_mask = CPU_MASK_NONE;
/*
* Increase the granularity value when there are more CPUs,
* because with more CPUs the 'effective latency' as visible
* to users decreases. But the relationship is not linear,
* so pick a second-best guess by going with the log2 of the
* number of CPUs.
*
* This idea comes from the SD scheduler of Con Kolivas:
*/
static inline void sched_init_granularity(void)
{
unsigned int factor = 1 + ilog2(num_online_cpus());
const unsigned long limit = 200000000;
sysctl_sched_min_granularity *= factor;
if (sysctl_sched_min_granularity > limit)
sysctl_sched_min_granularity = limit;
sysctl_sched_latency *= factor;
if (sysctl_sched_latency > limit)
sysctl_sched_latency = limit;
sysctl_sched_wakeup_granularity *= factor;
sysctl_sched_batch_wakeup_granularity *= factor;
}
#ifdef CONFIG_SMP
/*
* This is how migration works:
@ -6688,10 +6714,12 @@ void __init sched_init_smp(void)
/* Move init over to a non-isolated CPU */
if (set_cpus_allowed(current, non_isolated_cpus) < 0)
BUG();
sched_init_granularity();
}
#else
void __init sched_init_smp(void)
{
sched_init_granularity();
}
#endif /* CONFIG_SMP */

18
kernel/sched_fair.c
View file

@ -22,7 +22,7 @@
/*
* Targeted preemption latency for CPU-bound tasks:
* (default: 20ms, units: nanoseconds)
* (default: 20ms * ilog(ncpus), units: nanoseconds)
*
* NOTE: this latency value is not the same as the concept of
* 'timeslice length' - timeslices in CFS are of variable length
@ -32,18 +32,18 @@
* (to see the precise effective timeslice length of your workload,
* run vmstat and monitor the context-switches (cs) field)
*/
const_debug unsigned int sysctl_sched_latency = 20000000ULL;
unsigned int sysctl_sched_latency = 20000000ULL;
/*
* Minimal preemption granularity for CPU-bound tasks:
* (default: 1 msec, units: nanoseconds)
* (default: 1 msec * ilog(ncpus), units: nanoseconds)
*/
const_debug unsigned int sysctl_sched_min_granularity = 1000000ULL;
unsigned int sysctl_sched_min_granularity = 1000000ULL;
/*
* is kept at sysctl_sched_latency / sysctl_sched_min_granularity
*/
const_debug unsigned int sched_nr_latency = 20;
unsigned int sched_nr_latency = 20;
/*
* After fork, child runs first. (default) If set to 0 then
@ -61,23 +61,23 @@ unsigned int __read_mostly sysctl_sched_compat_yield;
/*
* SCHED_BATCH wake-up granularity.
* (default: 10 msec, units: nanoseconds)
* (default: 10 msec * ilog(ncpus), units: nanoseconds)
*
* This option delays the preemption effects of decoupled workloads
* and reduces their over-scheduling. Synchronous workloads will still
* have immediate wakeup/sleep latencies.
*/
const_debug unsigned int sysctl_sched_batch_wakeup_granularity = 10000000UL;
unsigned int sysctl_sched_batch_wakeup_granularity = 10000000UL;
/*
* SCHED_OTHER wake-up granularity.
* (default: 10 msec, units: nanoseconds)
* (default: 10 msec * ilog(ncpus), units: nanoseconds)
*
* This option delays the preemption effects of decoupled workloads
* and reduces their over-scheduling. Synchronous workloads will still
* have immediate wakeup/sleep latencies.
*/
const_debug unsigned int sysctl_sched_wakeup_granularity = 10000000UL;
unsigned int sysctl_sched_wakeup_granularity = 10000000UL;
const_debug unsigned int sysctl_sched_migration_cost = 500000UL;