linux-kernel - Re: [PATCH 2/3] cpuacct: Simplify cpuacct_stats

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Date:	Thu, 12 May 2016 09:47:47 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Zhao Lei <zhaolei@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/3] cpuacct: Simplify cpuacct_stats_show


* Zhao Lei <zhaolei@...fujitsu.com> wrote:

> Merge code for each cpustat(system/user) into a loop,
> to avoid clone of code blocks.
> Only a little cleanup.
> 
> Signed-off-by: Zhao Lei <zhaolei@...fujitsu.com>
> ---
>  kernel/sched/cpuacct.c | 29 ++++++++++++++---------------
>  1 file changed, 14 insertions(+), 15 deletions(-)

I see a couple of problems with this patch:

- please Cc: all scheduler maintainers to scheduler patches.

- please fix the title of the patch: have a look at 'git log 
  kernel/sched/cpuacct.c' how recent titles to that code look like.

- when referring to functions in changelogs, please add '()' to separate them from 
  variable and other names. I.e. it's "cpuacct_stats_show()".

>  static int cpuacct_stats_show(struct seq_file *sf, void *v)
>  {
>  	struct cpuacct *ca = css_ca(seq_css(sf));
> +	s64 val[CPUACCT_STAT_NSTATS];
>  	int cpu;
> -	s64 val = 0;
> +	int stat;
>  
> +	memset(val, 0, sizeof(val));
>  	for_each_possible_cpu(cpu) {
> -		struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat, cpu);
> -		val += kcpustat->cpustat[CPUTIME_USER];
> -		val += kcpustat->cpustat[CPUTIME_NICE];
> +		struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat,
> +							      cpu);

Horrible taste: in what universe is that linebreak an improvement to the code?

> +		val[CPUACCT_STAT_USER]   += kcpustat->cpustat[CPUTIME_USER];

Also, please put a newline between variable definitions and the first 
non-definition C statement...

> +		val[CPUACCT_STAT_USER]   += kcpustat->cpustat[CPUTIME_NICE];
> +		val[CPUACCT_STAT_SYSTEM] += kcpustat->cpustat[CPUTIME_SYSTEM];
> +		val[CPUACCT_STAT_SYSTEM] += kcpustat->cpustat[CPUTIME_IRQ];
> +		val[CPUACCT_STAT_SYSTEM] += kcpustat->cpustat[CPUTIME_SOFTIRQ];

Also, if you introduce a helper variable to shorten the code, you might as well 
introduce one for the cpustat array itself, and skip the whole 'kcpustat->' 
repetition ...

Thanks,

	Ingo