linux-kernel - wrong count of CPU usage

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Message-ID: <CAAW1UO_8N-10gLzKp4gV-P3JGOsk-_QnZiedWjhw3rWe33fKjQ@mail.gmail.com>
Date:	Wed, 16 May 2012 18:33:35 +0400
From:	Azat Khuzhin <dohardgopro@...il.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: wrong count of CPU usage

Hi all

I have machine that have uptime 212 days, kernel version: Linux
2.6.35.14-97.fc14.x86_64 #1 SMP Sat Sep 17 00:15:37 UTC 2011 x86_64
x86_64 x86_64 GNU/Linux
Before top (1) utility shows some activity per process, as it should
be (sort by %CPU column)

But from some time, no activity in top (1) per process at all
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
    1 root      20   0 19420 1548 1240 S  0.0  0.0  17:48.09 init
    2 root      20   0     0    0    0 S  0.0  0.0   0:09.72 kthreadd
    3 root      20   0     0    0    0 S  0.0  0.0  20:34.76 ksoftirqd/0

But load avg > 10
top (1) shows some activity on cores (I mean not processes, that
created by kernel)
top - 09:58:26 up 212 days,  7:06,  8 users,  load average: 13.27, 12.20, 11.37
Tasks: 815 total,   9 running, 803 sleeping,   2 stopped,   1 zombie
Cpu0  : 47.5%us,  8.0%sy,  0.3%ni, 26.4%id, 16.9%wa,  0.0%hi,  0.9%si,  0.0%st
Cpu1  : 39.7%us,  5.2%sy,  0.0%ni, 48.0%id,  6.8%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu2  : 29.8%us,  3.1%sy,  0.0%ni, 59.7%id,  7.4%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu3  : 15.9%us,  2.8%sy,  0.0%ni, 77.3%id,  3.7%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu4  : 39.3%us,  5.2%sy,  0.0%ni, 37.4%id, 17.8%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu5  : 29.6%us,  4.0%sy,  0.0%ni, 62.3%id,  3.7%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu6  : 20.4%us,  5.0%sy,  0.0%ni, 74.3%id,  0.0%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu7  : 17.3%us,  2.8%sy,  0.0%ni, 76.8%id,  3.1%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu8  : 32.8%us,  6.5%sy,  0.0%ni, 31.6%id, 29.1%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu9  : 27.6%us,  3.1%sy,  0.0%ni, 69.3%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu10 :  6.8%us,  2.5%sy,  0.0%ni, 87.9%id,  2.8%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu11 :  8.7%us,  1.9%sy,  0.0%ni, 89.4%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu12 : 27.3%us,  2.8%sy,  0.0%ni, 52.8%id, 17.1%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu13 : 18.2%us,  3.7%sy,  0.0%ni, 77.5%id,  0.6%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu14 : 21.4%us,  3.8%sy,  0.0%ni, 74.8%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu15 : 10.0%us,  1.9%sy,  0.0%ni, 87.9%id,  0.3%wa,  0.0%hi,  0.0%si,  0.0%st

So seems like after some time kernel not updating /proc/PID/stat properly

I wrote shell script (attach), that count CPU usage, and it also shows 0
This script base on 14, 15 columns from /proc/PID/stat (as man proc
says, that it utime and stime clocks, and /proc/stat summary), but for
newly created processes

Summarize
/proc/PID/stat seems not change counters utime, stime
/proc/stat updated

--
Azat Khuzhin

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