netdev - Re: [PATCH v4 5/7] sched/topology: Introduce sched_numa_hop

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Date:   Sun, 25 Sep 2022 08:24:41 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Tony Luck <tony.luck@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Gal Pressman <gal@...dia.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [PATCH v4 5/7] sched/topology: Introduce sched_numa_hop_mask()

On Sun, Sep 25, 2022 at 08:00:49AM -0700, Yury Norov wrote:
> On Fri, Sep 23, 2022 at 04:55:40PM +0100, Valentin Schneider wrote:
> > Tariq has pointed out that drivers allocating IRQ vectors would benefit
> > from having smarter NUMA-awareness - cpumask_local_spread() only knows
> > about the local node and everything outside is in the same bucket.
> > 
> > sched_domains_numa_masks is pretty much what we want to hand out (a cpumask
> > of CPUs reachable within a given distance budget), introduce
> > sched_numa_hop_mask() to export those cpumasks.
> > 
> > Link: http://lore.kernel.org/r/20220728191203.4055-1-tariqt@nvidia.com
> > Signed-off-by: Valentin Schneider <vschneid@...hat.com>
> > ---
> >  include/linux/topology.h | 12 ++++++++++++
> >  kernel/sched/topology.c  | 31 +++++++++++++++++++++++++++++++
> >  2 files changed, 43 insertions(+)
> > 
> > diff --git a/include/linux/topology.h b/include/linux/topology.h
> > index 4564faafd0e1..3e91ae6d0ad5 100644
> > --- a/include/linux/topology.h
> > +++ b/include/linux/topology.h
> > @@ -245,5 +245,17 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)
> >  	return cpumask_of_node(cpu_to_node(cpu));
> >  }
> >  
> > +#ifdef CONFIG_NUMA
> > +extern const struct cpumask *sched_numa_hop_mask(int node, int hops);
> > +#else
> > +static inline const struct cpumask *sched_numa_hop_mask(int node, int hops)
> > +{
> > +	if (node == NUMA_NO_NODE && !hops)
> > +		return cpu_online_mask;
> > +
> > +	return ERR_PTR(-EOPNOTSUPP);
> > +}
> > +#endif	/* CONFIG_NUMA */
> > +
> >  
> >  #endif /* _LINUX_TOPOLOGY_H */
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > index 8739c2a5a54e..ee77706603c0 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -2067,6 +2067,37 @@ int sched_numa_find_closest(const struct cpumask *cpus, int cpu)
> >  	return found;
> >  }
> >  
> > +/**
> > + * sched_numa_hop_mask() - Get the cpumask of CPUs at most @hops hops away.
> > + * @node: The node to count hops from.
> > + * @hops: Include CPUs up to that many hops away. 0 means local node.
> > + *
> > + * Requires rcu_lock to be held. Returned cpumask is only valid within that
> > + * read-side section, copy it if required beyond that.
> > + *
> > + * Note that not all hops are equal in distance; see sched_init_numa() for how
> > + * distances and masks are handled.
> > + *
> > + * Also note that this is a reflection of sched_domains_numa_masks, which may change
> > + * during the lifetime of the system (offline nodes are taken out of the masks).
> > + */
> 
> Since it's exported, can you declare function parameters and return
> values properly?

s/declare/describe