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Commit 19978ca6 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

sched: reintroduce SMP tunings again 



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

 |  commit 38ad464d
 |  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: default avatarIngo Molnar <mingo@elte.hu>
parent fa13a5a1

kernel/sched.c

+28 −0
Original line number Diff line number Diff line
@@ -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 */

kernel/sched_fair.c

+9 −9
Original line number Diff line number Diff line
@@ -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;