netdev - Re: [PATCH 3/9] sched: add sched_numa_find_nth

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Date:   Fri, 3 Feb 2023 08:58:23 +0800
From:   Chen Yu <yu.c.chen@...el.com>
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>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Gal Pressman <gal@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Haniel Bristot de Oliveira <bristot@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jacob Keller <jacob.e.keller@...el.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>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Peter Lafreniere <peter@...jl.ca>,
        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 3/9] sched: add sched_numa_find_nth_cpu()

On 2023-01-20 at 20:24:30 -0800, Yury Norov wrote:
> The function finds Nth set CPU in a given cpumask starting from a given
> node.
> 
> Leveraging the fact that each hop in sched_domains_numa_masks includes the
> same or greater number of CPUs than the previous one, we can use binary
> search on hops instead of linear walk, which makes the overall complexity
> of O(log n) in terms of number of cpumask_weight() calls.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> Acked-by: Tariq Toukan <tariqt@...dia.com>
> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> Reviewed-by: Peter Lafreniere <peter@...jl.ca>
> ---
>  include/linux/topology.h |  8 ++++++
>  kernel/sched/topology.c  | 57 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 65 insertions(+)
>
[snip] 
> + * sched_numa_find_nth_cpu() - given the NUMA topology, find the Nth next cpu
> + *                             closest to @cpu from @cpumask.
Just minor question, the @cpu below is used as the index, right? What does "close to @cpu"
mean above?
> + * cpumask: cpumask to find a cpu from
> + * cpu: Nth cpu to find
Maybe also add description for @node?

thanks,
Chenyu