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From: Albert Cahalan <albert@users.sf.net>
To: Nick Piggin <piggin@cyberone.com.au>
Cc: Albert Cahalan <albert@users.sourceforge.net>,
	linux-kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: decaying average for %CPU
Date: 16 Oct 2003 23:00:29 -0400	[thread overview]
Message-ID: <1066359629.15920.161.camel@cube> (raw)
In-Reply-To: <3F8F5A53.50209@cyberone.com.au>

On Thu, 2003-10-16 at 22:56, Nick Piggin wrote:
> Albert Cahalan wrote:
> 
> >The UNIX standard requires that Linux provide
> >some measure of a process's "recent" CPU usage.
> >Right now, it isn't provided. You might run a
> >CPU hog for a year, stop it ("kill -STOP 42")
> >for a few hours, and see that "ps" is still
> >reporting 99.9% CPU usage. This is because the
> >kernel does not provide a decaying average.
> 
> I think the kernel provides enough info for userspace to do
> the job, doesn't it?

I'm pretty sure not. Linux provides:

per-process start time
current time
per-process total (lifetime) CPU usage
units of time measurement (awkwardly)
boot time

>From that you can compute %CPU over the whole
life of the process. This does not meet the
requirements of the UNIX standard.

What we do for load average is about right,
except that per-process values can't all get
updated at the same time. So the algorithm
needs to be adjusted a bit to allow for that



  reply	other threads:[~2003-10-17  3:14 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-10-17  2:35 Albert Cahalan
2003-10-17  2:56 ` Nick Piggin
2003-10-17  3:00   ` Albert Cahalan [this message]
2003-10-17  3:21     ` Nick Piggin
2003-10-17  4:17       ` Albert Cahalan
2003-10-17 22:48         ` Nick Piggin

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