linux-kernel - Re: PM-Timer clock source is slow. Try something else: How slow? What other source(s)?

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Message-ID: <456E8181.4060109@in.ibm.com>
Date:	Thu, 30 Nov 2006 12:30:17 +0530
From:	Srinivasa Ds <srinivasa@...ibm.com>
To:	john stultz <johnstul@...ibm.com>
CC:	Linda Walsh <lkml@...nx.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: PM-Timer clock source is slow. Try something else: How slow?
 What other source(s)?

john stultz wrote:
> On Wed, 2006-11-29 at 16:56 -0800, Linda Walsh wrote:
>   
>> I recently noticed this message in my bootup that I don't remember
>> from before:
>>
>> PCI: Probing PCI hardware (bus 00)
>> * Found PM-Timer Bug on the chipset. Due to workarounds for a bug,
>> * this clock source is slow. Consider trying other clock sources
>>     
>
> This basically means that your chipset has a bug which requires the ACPI
> PM timer to be read three times in order to get a valid reading.
>
> This will cause gettimeofday/clock_gettime to take longer to execute,
> which is what is meant by "slow" (rather then the counter's frequency
> being incorrect).
>
>   
>>     How would this affect my clock?  It says to try another
>> clock source, what type of clock source would it be suggesting I
>> use? Another chip already in the computer? 
Yes.
>> It is an Intel 440BX
>> chipset; on an Dell motherboard. Would that be likely to have
>> another chip source that is compensating?
>>     
You can change the clock source using "clock=" kernel parameter. Please 
refer to  Documentation/kernel-parameters.txt file of kernel source.
>> I don't notice a significant clock slowdown, but I'm running NTP,
>> so that could be masking the problem.
>>     
>
> Unless you're running performance critical programs that utilize
> gettimeofday/clock_gettime, you probably won't notice anything. Time
> should still function properly.  If you are having performance issues,
> you can try using a different clocksource (the TSC is probably safe, but
> not necessarily).
>
> thanks
> -john
>
>
>
> -
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>   
Thanks
 Srinivasa DS
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