linux-kernel - Re: [PATCH] fix idle ticks in cpu summary line of /proc/stat

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Date:	Mon, 12 Mar 2012 10:17:39 -0400
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fix idle ticks in cpu summary line of /proc/stat

On Mon, 12 Mar 2012 13:17:26 +0100
Michal Hocko <mhocko@...e.cz> wrote:

> Goot catch. But I think that the following fix should be better because
> it doesn't change the semantic of the function. What do you think?
..
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 7656642..dec767f 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -221,7 +221,7 @@ u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
>  		update_ts_time_stats(cpu, ts, now, last_update_time);
>  		idle = ts->idle_sleeptime;
>  	} else {
> -		if (ts->idle_active && !nr_iowait_cpu(cpu)) {
> +		if (cpu_online(cpu) && ts->idle_active && !nr_iowait_cpu(cpu)) {
>  			ktime_t delta = ktime_sub(now, ts->idle_entrytime);
> 
>  			idle = ktime_add(ts->idle_sleeptime, delta);
> @@ -262,7 +262,7 @@ u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
>  		update_ts_time_stats(cpu, ts, now, last_update_time);
>  		iowait = ts->iowait_sleeptime;
>  	} else {
> -		if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
> +		if (cpu_online(cpu) && ts->idle_active && nr_iowait_cpu(cpu) > 0) {
>  			ktime_t delta = ktime_sub(now, ts->idle_entrytime);
> 
>  			iowait = ktime_add(ts->iowait_sleeptime, delta);

I would prefer an early exit from the functions. The target cpu is offline,
who guarantees that the "struct tick_sched" for the cpu contains anything
useful?

-- 
blue skies,
   Martin.

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


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