Am Mittwoch 09 September 2009 schrieb tip-bot for Mike Galbraith: > Commit-ID: 172e082a9111ea504ee34cbba26284a5ebdc53a7 > Gitweb: > http://git.kernel.org/tip/172e082a9111ea504ee34cbba26284a5ebdc53a7 > Author: Mike Galbraith <efault@xxxxxx> > AuthorDate: Wed, 9 Sep 2009 15:41:37 +0200 > Committer: Ingo Molnar <mingo@xxxxxxx> > CommitDate: Wed, 9 Sep 2009 17:30:06 +0200 > > 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@xxxxxx> > Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > LKML-Reference: <1252486344.28645.18.camel@xxxxxxxxxxxxxxxx> > Signed-off-by: Ingo Molnar <mingo@xxxxxxx> > > > --- > kernel/sched_fair.c | 12 ++++++------ > 1 files changed, 6 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > index af325a3..26fadb4 100644 > --- a/kernel/sched_fair.c > +++ b/kernel/sched_fair.c > @@ -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; Needs to be lower for a fluid desktop experience here: shambhala:/proc/sys/kernel> cat sched_min_granularity_ns 100000 > > /* > * 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; Dito: shambhala:/proc/sys/kernel> cat sched_wakeup_granularity_ns 100000 With shambhala:~> cat /proc/version Linux version 2.6.31-rc7-tp42-toi-3.0.1-04741-g57e61c0 (martin@shambhala) (gcc version 4.3.3 (Debian 4.3.3-10) ) #6 PREEMPT Sun Aug 23 10:51:32 CEST 2009 on my ThinkPad T42. Otherwise compositing animations like switching desktops and zooming in newly opening windows still appear jerky. Even with: shambhala:/sys/kernel/debug> cat sched_features NO_NEW_FAIR_SLEEPERS NO_NORMALIZED_SLEEPER ADAPTIVE_GRAN WAKEUP_PREEMPT START_DEBIT AFFINE_WAKEUPS CACHE_HOT_BUDDY SYNC_WAKEUPS NO_HRTICK NO_DOUBLE_TICK ASYM_GRAN LB_BIAS LB_WAKEUP_UPDATE ASYM_EFF_LOAD NO_WAKEUP_OVERLAP LAST_BUDDY OWNER_SPIN But NO_NEW_FAIR_SLEEPERS also gives a benefit. It makes those animation even more fluent. In complete I am quity happy with shambhala:/proc/sys/kernel> grep "" *sched* sched_child_runs_first:0 sched_compat_yield:0 sched_features:113916 sched_latency_ns:5000000 sched_migration_cost:500000 sched_min_granularity_ns:100000 sched_nr_migrate:32 sched_rt_period_us:1000000 sched_rt_runtime_us:950000 sched_shares_ratelimit:250000 sched_shares_thresh:4 sched_wakeup_granularity_ns:100000 for now. It really makes a *lot* of difference. But it appears that both sched_min_granularity_ns and sched_wakeup_granularity_ns have to be lower on my ThinkPad for best effect. I would still prefer some autotuning, where I say "desktop!" or nothing at all. And thats it. Ciao, -- Martin 'Helios' Steigerwald - http://www.Lichtvoll.de GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7
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