linux-kernel - Re: [PATCH 2/8] sched/topology: introduce sched_numa_find_next

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Message-ID: <ZDROvNNIPdahL3AP@yury-laptop>
Date:   Mon, 10 Apr 2023 11:00:28 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>,
        Pawel Chmielewski <pawel.chmielewski@...el.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Gal Pressman <gal@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Barry Song <baohua@...nel.org>
Subject: Re: [PATCH 2/8] sched/topology: introduce sched_numa_find_next_cpu()

On Mon, Mar 27, 2023 at 01:28:12PM +0300, Andy Shevchenko wrote:
> On Sat, Mar 25, 2023 at 11:55:08AM -0700, Yury Norov wrote:
> > The function searches for the next CPU in a given cpumask according to
> > NUMA topology, so that it traverses cpus per-hop.
> > 
> > If the CPU is the last cpu in a given hop, sched_numa_find_next_cpu()
> > switches to the next hop, and picks the first CPU from there, excluding
> > those already traversed.
> 
> ...
> 
> > +/*
> 
> Hmm... Is it deliberately not a kernel doc?

Yes, I'd prefer to encourage people to use for_each() approach instead
of calling it directly.

If there will be a good reason to make it a more self-consistent thing,
we'll have to add a wrapper, just like sched_numa_find_nth_cpu() is
wrapped with cpumask_local_spread(). Particularly, use RCU lock/unlock
and properly handle NUMA_NO_NODE.
 
> > + * sched_numa_find_next_cpu() - given the NUMA topology, find the next cpu
> > + * cpumask: cpumask to find a cpu from
> > + * cpu: current cpu
> > + * node: local node
> > + * hop: (in/out) indicates distance order of current CPU to a local node
> > + *
> > + * The function searches for next cpu at a given NUMA distance, indicated
> > + * by hop, and if nothing found, tries to find CPUs at a greater distance,
> > + * starting from the beginning.
> > + *
> > + * returns: cpu, or >= nr_cpu_ids when nothing found.
> > + */
> 
> -- 
> With Best Regards,
> Andy Shevchenko
>