Re: [PATCH v3 3/3] cpuacct: split usage into user_usage and sys_usage

From: Peter Zijlstra
Date: Thu Mar 17 2016 - 04:40:11 EST

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

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?