linux-kernel - Re: [PATCH v2 3/8] sched/topology: add for_each_numa

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Message-ID: <xhsmhv8hjj93z.mognet@vschneid.remote.csb>
Date:   Wed, 26 Apr 2023 10:17:20 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Yury Norov <yury.norov@...il.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>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.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>,
        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 v2 3/8] sched/topology: add for_each_numa_cpu() macro

On 25/04/23 22:32, Yury Norov wrote:
> On Tue, Apr 25, 2023 at 10:54:48AM +0100, Valentin Schneider wrote:
>> On 19/04/23 22:19, Yury Norov wrote:
>> > +/**
>> > + * for_each_numa_cpu - iterate over cpus in increasing order taking into account
>> > + *		       NUMA distances from a given node.
>> > + * @cpu: the (optionally unsigned) integer iterator
>> > + * @hop: the iterator variable, must be initialized to a desired minimal hop.
>> > + * @node: the NUMA node to start the search from.
>> > + * @mask: the cpumask pointer
>> > + *
>> > + * Requires rcu_lock to be held.
>> > + */
>> > +#define for_each_numa_cpu(cpu, hop, node, mask)					\
>> > +	for ((cpu) = 0, (hop) = 0;						\
>> > +		(cpu) = sched_numa_find_next_cpu((mask), (cpu), (node), &(hop)),\
>> > +		(cpu) < nr_cpu_ids;						\
>> > +		(cpu)++)
>> > +
>> 
>> I think we can keep sched_numa_find_next_cpu() as-is, but could we make
>> that macro use cpu_possible_mask by default? We can always add a variant
>> if/when we need to feed in a different mask.
>
> As mentioned in discussion to the driver's patch, all that numa things
> imply only online CPUs, so cpu_possible_mask may mislead to some extent. 
>
> Anyways, can you elaborate what you exactly want? Like this?
>
>  #define for_each_numa_online_cpu(cpu, hop, node)       \
>         for_each_numa_cpu(cpu, hop, node, cpu_online_mask)

Yeah, something like that. Like you said, the NUMA cpumasks built by the
scheduler reflect the online topology, so s/possible/online/ shouldn't
change much here.