linux-kernel - Re: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86

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Message-ID: <20080531211306.GM5405@ucw.cz>
Date:	Sat, 31 May 2008 23:13:06 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	venkatesh.pallipadi@...el.com, suresh.b.siddha@...el.com,
	Michael Neuling <mikey@...ling.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86

Hi!

> > entitlement for the process as per the current CPU frequency.  This
> > technique is used in powerpc architecture with the help of hardware
> > registers that accurately capture the entitlement.
> > 
> 
> there are some issues with this unfortunately, and these make it
> a very complex thing to do. 
> Just to mention a few:
> 1) What if the BIOS no longer allows us to go to the max frequency for
> a period (for example as a result of overheating); with the approach
> above, the admin would THINK he can go faster, but he cannot in reality,
> so there's misleading information (the system looks half busy, while in

Plus time one-second-computation-job returning anything else is just
wrong. Even when it only happens when overheated... or only on battery
power.

If you want scaled utime, you need new interface.

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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