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SubjectRe: [PATCH] sched/topology: Remove redundant variable and fix incorrect type in build_sched_domains
On Fri, Mar 04, 2022 at 12:56:44PM +0000, Valentin Schneider wrote:
> On 18/02/22 21:57, K Prateek Nayak wrote:
> > While investigating the sparse warning reported by the LKP bot [1],
> > observed that we have a redundant variable "top" in the function
> > build_sched_domains that was introduced in the recent commit
> > e496132ebedd ("sched/fair: Adjust the allowed NUMA imbalance when
> > SD_NUMA spans multiple LLCs")
> >
> > The existing variable "sd" suffices which allows us to remove the
> > redundant variable "top" while annotating the other variable "top_p"
> > with the "__rcu" annotation to silence the sparse warning.
> >
> > [1] https://lore.kernel.org/lkml/202202170853.9vofgC3O-lkp@intel.com/
> >
> > Fixes: e496132ebedd ("sched/fair: Adjust the allowed NUMA imbalance when SD_NUMA spans multiple LLCs")
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
> > ---
> > kernel/sched/topology.c | 8 +++-----
> > 1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > index e6cd55951304..4b757fb8f661 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -2255,7 +2255,7 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
> >
> > if (!(sd->flags & SD_SHARE_PKG_RESOURCES) && child &&
> > (child->flags & SD_SHARE_PKG_RESOURCES)) {
> > - struct sched_domain *top, *top_p;
> > + struct sched_domain __rcu *top_p;
> > unsigned int nr_llcs;
> >
> > /*
> > @@ -2280,11 +2280,9 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
> > sd->imb_numa_nr = imb;
> >
> > /* Set span based on the first NUMA domain. */
> > - top = sd;
> > - top_p = top->parent;
> > + top_p = sd->parent;
> > while (top_p && !(top_p->flags & SD_NUMA)) {
> > - top = top->parent;
> > - top_p = top->parent;
> > + top_p = top_p->parent;
> > }
> > imb_span = top_p ? top_p->span_weight : sd->span_weight;
>
>
> So sd starts as the first domain without SD_SHARE_PKG_RESOURCES (but its
> direct child has it), and the loop searches upward for a NUMA domain. This
> indeed shouldn't require two variables.
>
> I was going to say that while you're at it, you could init top_p to sd
> rather than sd->parent in case someone runs a non-default
> sched_domain_topology[], but NODE should have neither
> SD_SHARE_PKG_RESOURCES nor SD_NUMA, so that doesn't seem required.
>
> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

Thanks!

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