linux-kernel - Re: [patch] s390/smp: clean up a condition

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Date:	Mon, 18 Jul 2016 09:07:35 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] s390/smp: clean up a condition

On Thu, 14 Jul 2016 13:40:22 +0300
Dan Carpenter <dan.carpenter@...cle.com> wrote:

> I can never remember precedence rules.  Let's add some parenthesis so
> this code is more clear.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> The original code is correct right?  We didn't intend to say:
> 
> 	sclp_max = sclp.max_cores * (sclp_max ?: nr_cpu_ids);
> 
> diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
> index 5c8f7ca..35531fe 100644
> --- a/arch/s390/kernel/smp.c
> +++ b/arch/s390/kernel/smp.c
> @@ -887,7 +887,7 @@ void __init smp_fill_possible_mask(void)
> 
>  	sclp_max = max(sclp.mtid, sclp.mtid_cp) + 1;
>  	sclp_max = min(smp_max_threads, sclp_max);
> -	sclp_max = sclp.max_cores * sclp_max ?: nr_cpu_ids;
> +	sclp_max = (sclp.max_cores * sclp_max) ?: nr_cpu_ids;
>  	possible = setup_possible_cpus ?: nr_cpu_ids;
>  	possible = min(possible, sclp_max);
>  	for (cpu = 0; cpu < possible && cpu < nr_cpu_ids; cpu++)
> 

The code calculates the number of threads to use, then multiplies
it with the number of cores to get the number of logical CPUs.
If the product happens to be zero because the number of cores
could not be determined, then nr_cpu_ids is going to be used.

So the code is correct but with the parenthesis it is easier to
read. Applied & thanks.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.