Messages in this thread | | | Date | Thu, 13 Nov 2008 12:10:40 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] accelerate newidle balancing in relax_domain |
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* Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> wrote:
> Increasing the value of 'sched_relax_domain_level' in cpuset expands > the searching range of task balancing on some schedule events. As > the result it makes the task balancing in the range more aggressive, > so it will benefit some situation, such as where the latency is > required even it sacrifices cache hit rate etc. (for such situation, > it would be ideally best that cpus do not be idle until there are no > runnable task.) > > This patch aimed to accelerate the balancing in the relax_domain. > > The newidle balancing is kicked when tasks in a runqueue run out. It > finds and pulls runnable tasks from other busy cpus, checking load > imbalance between cpus. Considering above situation, using loads in > short term is preferred than that in long term because it makes > balancing more aggressive otherwise it becomes relatively > conservative. The referenced load is selected by the newidle_idx > parameter of scheduler domains, so this patch tunes the parameters > only when domains are in the relax_domain's range. There are no > effects if you don't use relax_domain. > > Following is a result of my short-lightweight-transaction test, showing > average of requester's latency (ms), 300 couple of threads running 30 sec > on 8cpu/Itanium: > > 1) v2.6.28-rc4 > Average 0.748783 Std Div 1.688022 Throughput 165313 > 2) v2.6.28-rc4 + relax_domain > Average 0.536867 Std Div 1.115383 Throughput 168492 > 3) v2.6.28-rc4 + relax_domain + patch > Average 0.385164 Std Div 0.801875 Throughput 170069
that improvement in metric looks good.
> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> > --- > kernel/sched.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched.c b/kernel/sched.c > index 57c933f..c970239 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -7366,6 +7366,8 @@ static void set_domain_attribute(struct sched_domain *sd, > } else { > /* turn on idle balance on this domain */ > sd->flags |= (SD_WAKE_IDLE_FAR|SD_BALANCE_NEWIDLE); > + /* make newidle balancing more aggressive */ > + sd->newidle_idx = 0;
I agree with making it more sensitive to momentary load fluctuations. (as long as other metrics do not degrade).
But this solutin basically overrides the newidle_idx tuning in topology.h.
Is there a strong reason to do this tuning dynamically, or could we just decrease newidle_idx in the appropriate templates in the topology.h files?
Ingo
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