linux-kernel - Re: Question about /proc/uptime

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Message-ID: <20131227144504.GA17192@redhat.com>
Date:	Fri, 27 Dec 2013 15:45:04 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Rob Landley <rob@...dley.net>
Cc:	linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: Question about /proc/uptime

Add Frederic, I am not sure I understand this correctly.

On 12/25, Rob Landley wrote:
>
> There are two values here, the first is seconds since boot time (which
> is just elapsed time; at one point it was ajusted for suspend and that
> was revered as confusing).

Hmm, uptime_proc_show() still uses get_monotonic_boottime(), this should
include suspend time?

> The second value isn't documented but looking at fs/proc/uptime.c I
> think it's idle time?

And this cpustat[CPUTIME_IDLE] doesn't match get_idle_time(), I guess
it only counts ticks.

> Except, if yo uadd up the idle time from all
> processors wouldn't you get 4x the uptime on a 4-way SMP system that's
> been idle since boot?

Yes, looks strange.

> Also, is this actual "cpu was on but not doing anything" time, so
> doesn't count suspend as idle?

I think suspend is not counted as idle.

> Confused,

I guess the 2nd value is historical, probably you should use /proc/stat.

Oleg.

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