linux-kernel - Re: [PATCH v3 5/5] lib/cpumask: reorganize cpumask_local

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Date:   Thu, 08 Dec 2022 20:17:22 +0000
From:   Peter Lafreniere <peter@...jl.ca>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Barry Song <baohua@...nel.org>,
        Ben Segall <bsegall@...gle.com>,
        haniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Gal Pressman <gal@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Saeed Mahameed <saeedm@...dia.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Tariq Toukan <ttoukan.linux@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org
Subject: Re: [PATCH v3 5/5] lib/cpumask: reorganize cpumask_local_spread() logic

> Now after moving all NUMA logic into sched_numa_find_nth_cpu(),
> else-branch of cpumask_local_spread() is just a function call, and
> we can simplify logic by using ternary operator.
>
> While here, replace BUG() with WARN().
Why make this change? It's still as bad to hit the WARN_ON as it was before.

> Signed-off-by: Yury Norov yury.norov@...il.com
>
> ---
> lib/cpumask.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/lib/cpumask.c b/lib/cpumask.c
> index 255974cd6734..c7029fb3c372 100644
> --- a/lib/cpumask.c
> +++ b/lib/cpumask.c
> @@ -127,16 +127,12 @@ unsigned int cpumask_local_spread(unsigned int i, int node)
> /* Wrap: we always want a cpu. */
> i %= num_online_cpus();
>
> - if (node == NUMA_NO_NODE) {
> - cpu = cpumask_nth(i, cpu_online_mask);
> - if (cpu < nr_cpu_ids)
> - return cpu;
> - } else {
> - cpu = sched_numa_find_nth_cpu(cpu_online_mask, i, node);
> - if (cpu < nr_cpu_ids)
> - return cpu;
> - }
> - BUG();
> + cpu = node == NUMA_NO_NODE ?
> + cpumask_nth(i, cpu_online_mask) :
> + sched_numa_find_nth_cpu(cpu_online_mask, i, node);
I find the if version clearer, and cleaner too if you drop the brackets.

For the ternary version it would be nice to parenthesize the equality
like you did in cmp() in 3/5.

> +
> + WARN_ON(cpu >= nr_cpu_ids);
>
> + return cpu;
> }
> EXPORT_SYMBOL(cpumask_local_spread);
>
> --
> 2.34.1

Minor nit: cmp() in 3/5 could use a longer name. The file's long, and
cmp() doesn't explain _what_ it's comparing. How about cmp_cpumask() or
something related to the function using it?

Other than the above particularities, the whole series looks good to me.
Reviewed-by: Peter Lafreniere <peter@...jl.ca>