linux-kernel - Re: [PATCH v3 3/3] cpuacct: split usage into user_usage and sys

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Message-ID: <20160317084002.GN6344@twins.programming.kicks-ass.net>
Date:	Thu, 17 Mar 2016 09:40:02 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Zhao Lei <zhaolei@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <htejun@...il.com>,
	Yang Dongsheng <yangds.fnst@...fujitsu.com>
Subject: Re: [PATCH v3 3/3] cpuacct: split usage into user_usage and sys_usage

On Thu, Mar 17, 2016 at 12:19:44PM +0800, Zhao Lei wrote:
> +static u64 __cpuusage_read(struct cgroup_subsys_state *css,
> +			   enum cpuacct_usage_index index)
>  {
>  	struct cpuacct *ca = css_ca(css);
>  	u64 totalcpuusage = 0;
>  	int i;
>  
>  	for_each_present_cpu(i)
> +		totalcpuusage += cpuacct_cpuusage_read(ca, i, index);
>  
>  	return totalcpuusage;
>  }

Ok, so while looking over this, it mostly uses for_each_present_cpu(),
which is already dubious, but then cpuacct_stats_show() uses
for_each_online_cpu().

Why is this? Why not always for_each_possible_cpu()?

Surely, if you offline a cpu, you still want its stat to be included in
your totals, otherwise your numbers will go backwards when you take a
cpu offline.

Could you double check the logic and maybe fix?

Thanks!