linux-kernel - Re: [PATCH] Re: /proc/uptime idle counter remains at 0

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Date:	Mon, 11 May 2009 09:42:03 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
cc:	Michael Abbott <michael@...neidae.co.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Re: /proc/uptime idle counter remains at 0


On Monday 2009-05-11 09:35, Martin Schwidefsky wrote:
>> I have to confess I don't really understand the logic of what's going on 
>> here -- in particular, what does the idle process do other than account 
>> for time when the processor has nothing useful to do?  It does seem to me 
>> now that the .utime and .stime fields are now less than useful -- maybe 
>> they can be deleted now?
>
>The idle task does not just sleep, it will do "real" work, e.g. softirq
>handling for interrupts / network traffic.

With an RT kernel, SIRQ and such are separate tasks. That should also
be play a role while 0 is displayed.

>> I've always assumed that the second field of /proc/uptime was a simple 
>> measure of time not spent doing real work, in other words a crude measure 
>> of spare CPU resources.  My instrument basically uses the the two fields 
>> of this file to compute a measure of CPU loading so it can raise an alert 
>> if the CPU doesn't have enough spare (idle) capacity.
>
>But it wasn't.. the old style stime of idle is a mixture of true idle
>time and some system time.

Then I would say let's show the idle time only (but still inculde
the idle time when the CPU is halted).

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