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From:   Valentin Schneider <vschneid@redhat.com>
To:     Yury Norov <yury.norov@gmail.com>
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        Barry Song <baohua@kernel.org>
Subject: Re: [PATCH v2 3/8] sched/topology: add for_each_numa_cpu() macro
In-Reply-To: <ZEi3dLvlg/35DUrM@yury-ThinkPad>
References: <20230420051946.7463-1-yury.norov@gmail.com>
 <20230420051946.7463-4-yury.norov@gmail.com>
 <xhsmh4jp4l21j.mognet@vschneid.remote.csb>
 <ZEi3dLvlg/35DUrM@yury-ThinkPad>
Date:   Wed, 26 Apr 2023 10:17:20 +0100
Message-ID: <xhsmhv8hjj93z.mognet@vschneid.remote.csb>
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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.