linux-kernel - Re: [PATCH v5 2/3] sched/topology: Introduce for_each_numa_hop

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Date:   Fri, 21 Oct 2022 16:16:17 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.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>,
        Yury Norov <yury.norov@...il.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 v5 2/3] sched/topology: Introduce for_each_numa_hop_mask()

On Fri, Oct 21, 2022 at 01:19:26PM +0100, Valentin Schneider wrote:
> The recently introduced sched_numa_hop_mask() exposes cpumasks of CPUs
> reachable within a given distance budget, wrap the logic for iterating over
> all (distance, mask) values inside an iterator macro.

...

>  #ifdef CONFIG_NUMA
> -extern const struct cpumask *sched_numa_hop_mask(int node, int hops);
> +extern const struct cpumask *sched_numa_hop_mask(unsigned int node, unsigned int hops);
>  #else
> -static inline const struct cpumask *sched_numa_hop_mask(int node, int hops)
> +static inline const struct cpumask *
> +sched_numa_hop_mask(unsigned int node, unsigned int hops)
>  {
> -	if (node == NUMA_NO_NODE && !hops)
> -		return cpu_online_mask;
> -
>  	return ERR_PTR(-EOPNOTSUPP);
>  }
>  #endif	/* CONFIG_NUMA */

I didn't get how the above two changes are related to the 3rd one which
introduces a for_each type of macro.

If you need change int --> unsigned int, perhaps it can be done in a separate
patch.

The change inside inliner I dunno about. Not an expert.

...

> +#define for_each_numa_hop_mask(mask, node)				     \
> +	for (unsigned int __hops = 0;					     \
> +	     /*								     \
> +	      * Unsightly trickery required as we can't both initialize	     \
> +	      * @mask and declare __hops in for()'s first clause	     \
> +	      */							     \
> +	     mask = __hops > 0 ? mask :					     \
> +		    node == NUMA_NO_NODE ?				     \
> +		    cpu_online_mask : sched_numa_hop_mask(node, 0),	     \
> +	     !IS_ERR_OR_NULL(mask);					     \

> +	     __hops++,							     \
> +	     mask = sched_numa_hop_mask(node, __hops))

This can be unified with conditional, see for_each_gpio_desc_with_flag() as
example how.

-- 
With Best Regards,
Andy Shevchenko