linux-kernel - Re: top displaying 9999% CPU usage

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Date:	Wed, 3 Oct 2007 16:04:07 +0200
From:	Frans Pop <elendil@...net.nl>
To:	linux-kernel@...r.kernel.org
Cc:	"Alexander E. Patrakov" <patrakov@....usu.ru>
Subject: Re: top displaying 9999% CPU usage

On Wednesday 03 October 2007, you wrote:
> Try to capture the i/o log with the following command:
> strace -o top.log top

Thanks for the suggestion.

> This will show for sure whether the kernel gives out incorrect data or
> top misinterprets them.

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
5269 fjp       20   0  442m  61m  33m S 9999  3.1   0:34.12 kontact

Here are the last two reads for PID 5269 from /proc before that:

15:48:51 stat("/proc/5269", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0
15:48:51 open("/proc/5269/stat", O_RDONLY) = 10
15:48:51 read(10, "5269 (kontact) S 1 5100 5100 0 -1 4202560 58186 7891 290 1 2911 502 10 15 20 0 6 0 9225 464408576 15694 18446744073709551615 4194304 4365900 140733817144688 18446744073709551615 47998530367074 0 0 4098 83113 18446744073709551615 0 0 17 1 0 0 0\n", 1023) = 244
15:48:51 open("/proc/5269/statm", O_RDONLY) = 10
15:48:54 stat("/proc/5269", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0
15:48:54 open("/proc/5269/stat", O_RDONLY) = 10
15:48:54 read(10, "5269 (kontact) S 1 5100 5100 0 -1 4202560 58186 7891 290 1 2912 500 10 15 20 0 6 0 9225 464408576 15694 18446744073709551615 4194304 4365900 140733817144688 18446744073709551615 47998530367074 0 0 4098 83113 18446744073709551615 0 0 17 1 0 0 0\n", 1023) = 244
15:48:54 open("/proc/5269/statm", O_RDONLY) = 10

The only change is in 2 consecutive columns: "2911 502" -> "2912 500".
Is processor usage calculated from those? Can someone explain how?

In reply to Jan Engelhardt:
If I run the endless loop, top just displays 100%.
I've not seen the 9999 in htop, only occasionally "100." for both.

This is on an x86_64 SMP box.
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