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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>
This commit is contained in:
Mike Galbraith 2009-09-09 15:41:37 +02:00 committed by Ingo Molnar
parent 2bba22c50b
commit 172e082a91
1 changed files with 6 additions and 6 deletions
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12
kernel/sched_fair.c
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@ -24,7 +24,7 @@
/*
* Targeted preemption latency for CPU-bound tasks:
* (default: 20ms * (1 + ilog(ncpus)), units: nanoseconds)
* (default: 5ms * (1 + 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
@ -34,13 +34,13 @@
* (to see the precise effective timeslice length of your workload,
* run vmstat and monitor the context-switches (cs) field)
*/
unsigned int sysctl_sched_latency = 20000000ULL;
unsigned int sysctl_sched_latency = 5000000ULL;
/*
* Minimal preemption granularity for CPU-bound tasks:
* (default: 4 msec * (1 + ilog(ncpus)), units: nanoseconds)
* (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
*/
unsigned int sysctl_sched_min_granularity = 4000000ULL;
unsigned int sysctl_sched_min_granularity = 1000000ULL;
/*
* is kept at sysctl_sched_latency / sysctl_sched_min_granularity
@ -63,13 +63,13 @@ unsigned int __read_mostly sysctl_sched_compat_yield;
/*
* SCHED_OTHER wake-up granularity.
* (default: 5 msec * (1 + ilog(ncpus)), units: nanoseconds)
* (default: 1 msec * (1 + 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.
*/
unsigned int sysctl_sched_wakeup_granularity = 5000000UL;
unsigned int sysctl_sched_wakeup_granularity = 1000000UL;
const_debug unsigned int sysctl_sched_migration_cost = 500000UL;