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

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Message-ID: <48438E54.1000404@linux.vnet.ibm.com>
Date:	Mon, 02 Jun 2008 11:38:20 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Pavel Machek <pavel@...e.cz>
CC:	Arjan van de Ven <arjan@...radead.org>,
	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>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86

Pavel Machek wrote:
> 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.

We do have a new interface, two new parameters per-task utimescaled and
stimescaled. They already exist in task_struct. Ditto for the delay accounting
pieces. Did I misunderstand your need for a new interface? We still keep utime
and stime around.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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