linux-kernel - Re: 2.6.25.2 - Jiffies/Time jumping back and forth (Regereesion from 2.6.24)

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Message-ID: <4822F065.9080502@googlemail.com>
Date:	Thu, 08 May 2008 14:21:57 +0200
From:	Gabriel C <nix.or.die@...glemail.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Martin Knoblauch <spamtrap@...bisoft.de>,
	Bart Van Assche <bart.vanassche@...il.com>,
	linux-kernel@...r.kernel.org, hmh@....eng.br
Subject: Re: 2.6.25.2 - Jiffies/Time jumping back and forth (Regereesion from
 2.6.24)

Thomas Gleixner wrote:
> On Wed, 7 May 2008, Martin Knoblauch wrote:
>>> no this looks different. As soon as the timesource is detected, I see non-zero 
>>> timestamps
>>> in dmesg, but they look smaller and jump in both directions. And I have never 
>>> seen this before
>>> 2.6.25.
>>>
>>> It actually might be a good idea to get the dmesg output from 2.6.24.
>>>
>>> Cheers
>>> Martin
>>  interesting - maybe related to clocksources. The HPET seems to be detected later in 2.6.25:
>>
>> 2.6.24:
>>
>> [    0.000000] Initializing CPU#0
>> [    0.000000] PID hash table entries: 4096 (order: 12, 32768 bytes)
>> -->[    0.000000] hpet clockevent registered
>> -->[    0.000000] TSC calibrated against HPET
>  
>> 2.6.25.2:
>>
>> [    0.000000] Initializing CPU#0
>> [    0.000000] PID hash table entries: 4096 (order: 12, 32768 bytes)
>> -->[    0.000000] TSC calibrated against PM_TIMER
>  
> That's odd indeed. Is HPET not registered at all in 2.6.25 or does it just happen late ?
> 
> please provide the output of:
> /sys/devices/system/clocksource/clocksource0/available_clocksource
> /sys/devices/system/clocksource/clocksource0/current_clocksource

I was about to report / ask bout this issue too.

I see the same output for >=2.6.25 , TSC calibrated against PM_TIMER and not against HPET anymore.


[    0.000000] TSC calibrated against PM_TIMER
[    0.000016] time.c: Detected 2499.949 MHz processor.
...
[    0.000999] hpet clockevent registered

So it seems to register to late in >=2.6.25 kernels ?

cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc hpet acpi_pm jiffies

cat /sys/devices/system/clocksource/clocksource0/current_clocksource
tsc


> 
> Thanks,
> 	tglx


Regards,

Gabriel C
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