From: Pavel Machek <pavel@ucw.cz>
To: malc <av1474@comtv.ru>
Cc: Con Kolivas <kernel@kolivas.org>, linux-kernel@vger.kernel.org
Subject: Re: CPU load
Date: Wed, 14 Feb 2007 21:45:15 +0100 [thread overview]
Message-ID: <20070214204515.GA26153@elf.ucw.cz> (raw)
In-Reply-To: <Pine.LNX.4.64.0702141023000.672@home.oyster.ru>
Hi!
>
> >>>I have (had?) code that 'exploits' this. I believe I could eat 90% of cpu
> >>>without being noticed.
> >>
> >>Slightly changed version of hog(around 3 lines in total changed) does that
> >>easily on 2.6.18.3 on PPC.
> >>
> >>http://www.boblycat.org/~malc/apc/load-hog-ppc.png
> >
> >I guess it's worth mentioning this is _only_ about displaying the cpu
> >usage to
> >userspace, as the cpu scheduler knows the accounting of each task in
> >different ways. This behaviour can not be used to exploit the cpu scheduler
> >into a starvation situation. Using the discrete per process accounting to
> >accumulate the displayed values to userspace would fix this problem, but
> >would be expensive.
>
> Guess you are right, but, once again, the problem is not so much about
> fooling the system to do something or other, but confusing the user:
>
> a. Everything is fine - the load is 0%, the fact that the system is
> overheating and/or that some processes do not do as much as they
> could is probably due to the bad hardware.
>
> b. The weird load pattern must be the result of bugs in my code.
> (And then a whole lot of time/effort is poured into fixing the
> problem which is simply not there)
>
> The current situation ought to be documented. Better yet some flag
> can
It probably _is_ documented, somewhere :-). If you find nice place
where to document it (top manpage?) go ahead with the patch.
> be introduced somewhere in the system so that it exports realy values to
> /proc, not the estimations that are innacurate in some cases (like hog)
Patch would be welcome, but I do not think it will be easy.
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
next prev parent reply other threads:[~2007-02-14 20:47 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-12 5:33 CPU load 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 [this message]
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
-- strict thread matches above, loose matches on Subject: below --
2007-02-12 16:57 Andrew Burgess
2007-02-12 18:15 ` malc
2002-07-10 14:50 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
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