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authorIngo Molnar <mingo@elte.hu>2007-11-09 22:39:38 +0100
committerIngo Molnar <mingo@elte.hu>2007-11-09 22:39:38 +0100
commit19978ca610946ed57c071bad63f8f6642ca1298b (patch)
tree3bdbe89a249b6091fbd71653f106f486337ca3d6 /kernel
parentfa13a5a1f25f671d084d8884be96fc48d9b68275 (diff)
downloadlinux-19978ca610946ed57c071bad63f8f6642ca1298b.tar.bz2
sched: reintroduce SMP tunings again
Yanmin Zhang reported an aim7 regression and bisected it down to: | commit 38ad464d410dadceda1563f36bdb0be7fe4c8938 | 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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c28
-rw-r--r--kernel/sched_fair.c18
2 files changed, 37 insertions, 9 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 3f6bd1112900..69cae271c63b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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 */
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index c495dcf7031b..7264814ba62a 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -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;