Messages in this thread | | | Date | Wed, 24 Jul 2013 11:26:33 +0800 | From | Michael Wang <> | Subject | Re: [PATCH v2] sched: update_top_cache_domain only at the times of building sched domain. |
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Hi, Rakib
On 07/24/2013 01:42 AM, Rakib Mullick wrote: > Currently, update_top_cache_domain() is called whenever schedule domain is built or destroyed. But, the following > callpath shows that they're at the same callpath and can be avoided update_top_cache_domain() while destroying schedule > domain and update only at the times of building schedule domains. > > partition_sched_domains() > detach_destroy_domain() > cpu_attach_domain() > update_top_cache_domain()
IMHO, cpu_attach_domain() and update_top_cache_domain() should be paired, below patch will open a window which 'rq->sd == NULL' while 'sd_llc != NULL', isn't it?
I don't think we have the promise that before we rebuild the stuff correctly, no one will utilize 'sd_llc'...
Further more, what will happen if the old sd was freed after next rcu work cycle while 'sd_llc' still hold the reference for some victims?
Thus I do suggest we leave the things untouched since the benefit we get is too less, not worth the risk...
Regards, Michael Wang
> build_sched_domains() > cpu_attach_domain() > update_top_cache_domain() > > Changes since v1: use sd to determine when to skip, courtesy PeterZ > > Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com> > --- > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b7c32cb..387fb66 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5138,7 +5138,8 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu) > rcu_assign_pointer(rq->sd, sd); > destroy_sched_domains(tmp, cpu); > > - update_top_cache_domain(cpu); > + if (sd) > + update_top_cache_domain(cpu); > } > > /* cpus with isolated domains */ > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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