linux-kernel - Re: [RFC PATCH 2/6] cpumask: Purify cpumask

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Message-ID: <20190527083052.GR2623@hirez.programming.kicks-ass.net>
Date:   Mon, 27 May 2019 10:30:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH 2/6] cpumask: Purify cpumask_next()

On Sat, May 25, 2019 at 01:21:59AM -0700, Nadav Amit wrote:
> cpumask_next() has no side-effects. Mark it as pure.

It would be good to have a few word on why... because apparently you
found this makes a difference.

> Cc: "David S. Miller" <davem@...emloft.net>
> Signed-off-by: Nadav Amit <namit@...are.com>
> ---
>  include/linux/cpumask.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index 147bdec42215..20df46705f9c 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -209,7 +209,7 @@ static inline unsigned int cpumask_last(const struct cpumask *srcp)
>  	return find_last_bit(cpumask_bits(srcp), nr_cpumask_bits);
>  }
>  
> -unsigned int cpumask_next(int n, const struct cpumask *srcp);
> +unsigned int __pure cpumask_next(int n, const struct cpumask *srcp);
>  
>  /**
>   * cpumask_next_zero - get the next unset cpu in a cpumask
> -- 
> 2.20.1
>