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

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Date:	Thu, 8 May 2008 07:05:05 -0700 (PDT)
From:	Martin Knoblauch <spamtrap@...bisoft.de>
To:	Gabriel C <nix.or.die@...glemail.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	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)

----- Original Message ----

> 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
> Sent: Thursday, May 8, 2008 2:21:57 PM
> 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
> 
> 
on two different systems running 2.6.25.2:

ibm x3650(2xDualCore)
-------------------------------------
[root@...dm60 ~]# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc hpet acpi_pm jiffies
[root@...dm60 ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
tsc

HP Proliant DL-380G4 (2xSingleCore)
------------------------------------------------------------
[root@...dm52 ~]# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc hpet acpi_pm jiffies
[root@...dm52 ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
tsc

and on the DL380G4 running 2.6.24:
---------------------------------------------------------
[root@...dm52 ~]# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
hpet acpi_pm jiffies tsc
[root@...dm52 ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
hpet


Cheers
Martin
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