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Commit 172e082a authored by Mike Galbraith's avatar Mike Galbraith Committed by Ingo Molnar
Browse files

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: default avatarMike Galbraith <efault@gmx.de>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1252486344.28645.18.camel@marge.simson.net>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2bba22c5

kernel/sched_fair.c

+6 −6
Original line number Diff line number Diff line
@@ -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;