sched: Re-tune the scheduler latency defaults to decrease worst-case latencies
Reduce the latency target from 20 msecs to 5 msecs. Why? Larger latencies increase spread, which is good for scaling, but bad for worst case latency. We still have the ilog(nr_cpus) rule to scale up on bigger server boxes. Signed-off-by: Mike Galbraith <efault@gmx.de> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1252486344.28645.18.camel@marge.simson.net> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -24,7 +24,7 @@
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/*
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/*
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* Targeted preemption latency for CPU-bound tasks:
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* Targeted preemption latency for CPU-bound tasks:
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* (default: 20ms * (1 + ilog(ncpus)), units: nanoseconds)
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* (default: 5ms * (1 + ilog(ncpus)), units: nanoseconds)
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*
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*
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* NOTE: this latency value is not the same as the concept of
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* NOTE: this latency value is not the same as the concept of
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* 'timeslice length' - timeslices in CFS are of variable length
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* 'timeslice length' - timeslices in CFS are of variable length
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@ -34,13 +34,13 @@
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* (to see the precise effective timeslice length of your workload,
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* (to see the precise effective timeslice length of your workload,
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* run vmstat and monitor the context-switches (cs) field)
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* run vmstat and monitor the context-switches (cs) field)
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*/
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*/
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unsigned int sysctl_sched_latency = 20000000ULL;
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unsigned int sysctl_sched_latency = 5000000ULL;
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/*
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/*
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* Minimal preemption granularity for CPU-bound tasks:
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* Minimal preemption granularity for CPU-bound tasks:
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* (default: 4 msec * (1 + ilog(ncpus)), units: nanoseconds)
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* (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
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*/
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*/
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unsigned int sysctl_sched_min_granularity = 4000000ULL;
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unsigned int sysctl_sched_min_granularity = 1000000ULL;
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/*
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/*
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* is kept at sysctl_sched_latency / sysctl_sched_min_granularity
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* is kept at sysctl_sched_latency / sysctl_sched_min_granularity
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@ -63,13 +63,13 @@ unsigned int __read_mostly sysctl_sched_compat_yield;
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/*
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/*
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* SCHED_OTHER wake-up granularity.
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* SCHED_OTHER wake-up granularity.
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* (default: 5 msec * (1 + ilog(ncpus)), units: nanoseconds)
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* (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
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*
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*
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* This option delays the preemption effects of decoupled workloads
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* This option delays the preemption effects of decoupled workloads
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* and reduces their over-scheduling. Synchronous workloads will still
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* and reduces their over-scheduling. Synchronous workloads will still
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* have immediate wakeup/sleep latencies.
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* have immediate wakeup/sleep latencies.
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*/
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*/
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unsigned int sysctl_sched_wakeup_granularity = 5000000UL;
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unsigned int sysctl_sched_wakeup_granularity = 1000000UL;
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const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
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const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
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