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* CPU load
@ 2002-07-10 14:50 David Chow
  2002-07-10 16:54 ` William Lee Irwin III
  0 siblings, 1 reply; 25+ messages in thread
From: David Chow @ 2002-07-10 14:50 UTC (permalink / raw)
  To: linux-kernel

Dear all,

Is there any calls in the kernel space I can determine the current
system load or CPU load?

regards,
David




^ permalink raw reply	[flat|nested] 25+ messages in thread
* CPU load
@ 2007-02-12  5:33 Vassili Karpov
  2007-02-12  5:44 ` Con Kolivas
  0 siblings, 1 reply; 25+ messages in thread
From: Vassili Karpov @ 2007-02-12  5:33 UTC (permalink / raw)
  To: linux-kernel

Hello,

How does the kernel calculates the value it places in `/proc/stat' at
4th position (i.e. "idle: twiddling thumbs")?

For background information as to why this question arose in the first
place read on.

While writing the code dealing with video acquisition/processing at
work noticed that what top(1) (and every other tool that uses
`/proc/stat' or `/proc/uptime') shows some very strange results.

Top claimed that the system running one version of the code[A] is
idling more often than the code[B] doing the same thing but more
cleverly. After some head scratching one of my colleagues suggested a
simple test that was implemented in a few minutes.

The test consisted of a counter that incremented in an endless loop
also after certain period of time had elapsed it printed the value of
the counter.  Running this test (with priority set to the lowest
possible level) with code[A] and code[B] confirmed that code[B] is
indeed faster than code[A], in a sense that the test made more forward
progress while code[B] is running.

Hard-coding some things (i.e. the value of the counter after counting
for the duration of one period on completely idle system) we extended
the test to show the percentage of CPU that was utilized. This never
matched the value that top presented us with.

Later small kernel module was developed that tried to time how much
time is spent in the idle handler inside the kernel and exported this
information to the user-space. The results were consistent with our
expectations and the output of the test utility.

Two more points.

a. In the past (again video processing context) i have witnessed
   `/proc/stat' claiming that CPU utilization is 0% for, say, 20
   seconds followed by 5 seconds of 30% load, and then the cycle
   repeated. According to the methods outlined above the load is
   always at 30%.

b. In my personal experience difference between `/proc/stat' and
   "reality" can easily reach 40% (think i saw even more than that)

The module and graphical application that uses it, along with some
short README and a link to Usenet article dealing with the same
subject is available at:
http://www.boblycat.org/~malc/apc

Thanks



^ permalink raw reply	[flat|nested] 25+ messages in thread
* Re: CPU load
@ 2007-02-12 16:57 Andrew Burgess
  2007-02-12 18:15 ` malc
  0 siblings, 1 reply; 25+ messages in thread
From: Andrew Burgess @ 2007-02-12 16:57 UTC (permalink / raw)
  To: av1474, linux-kernel

On 12/02/07, Vassili Karpov <av1474@comtv.ru> wrote:
>
> How does the kernel calculates the value it places in `/proc/stat' at
> 4th position (i.e. "idle: twiddling thumbs")?
>
..
>
> Later small kernel module was developed that tried to time how much
> time is spent in the idle handler inside the kernel and exported this
> information to the user-space. The results were consistent with our
> expectations and the output of the test utility.
..
> http://www.boblycat.org/~malc/apc

Vassili

Could you rewrite this code as a kernel patch for
discussion/inclusion in mainline? I and maybe others would
appreciate having idle statistics be more accurate.

Thanks for your work
Andrew


^ permalink raw reply	[flat|nested] 25+ messages in thread

end of thread, other threads:[~2007-02-26 16:42 UTC | newest]

Thread overview: 25+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2002-07-10 14:50 CPU load David Chow
2002-07-10 16:54 ` William Lee Irwin III
2002-07-10 17:49   ` Robert Love
2002-07-26 17:38     ` David Chow
2007-02-12  5:33 Vassili Karpov
2007-02-12  5:44 ` Con Kolivas
2007-02-12  5:54   ` malc
2007-02-12  6:12     ` Con Kolivas
2007-02-12  7:10       ` malc
2007-02-12  7:29         ` Con Kolivas
2007-02-12  5:55   ` Stephen Rothwell
2007-02-12  6:08     ` Con Kolivas
2007-02-12 14:32   ` Pavel Machek
2007-02-13 22:01     ` malc
2007-02-13 22:08       ` Con Kolivas
2007-02-14  7:28         ` malc
2007-02-14  8:09           ` Con Kolivas
2007-02-14 20:45           ` Pavel Machek
2007-02-25 10:35             ` malc
2007-02-26  9:28               ` Pavel Machek
2007-02-26 10:42                 ` malc
2007-02-26 16:38                   ` Randy Dunlap
2007-02-12 18:05   ` malc
2007-02-12 16:57 Andrew Burgess
2007-02-12 18:15 ` malc

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