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

Martin Knoblauch
2008-05-08T14:05:25Z

> From: Gabriel C <nix.or.die@googlemail.com>
> To: Thomas Gleixner <tglx@linutronix.de>
> Cc: Martin Knoblauch <spamtrap@knobisoft.de>; Bart Van Assche <bart.vanassche@gmail.com>; linux-kernel@vger.kernel.org; hmh@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@lpsdm60 ~]# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc hpet acpi_pm jiffies
[root@lpsdm60 ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
tsc

HP Proliant DL-380G4 (2xSingleCore)
------------------------------------------------------------
[root@lpsdm52 ~]# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc hpet acpi_pm jiffies
[root@lpsdm52 ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
tsc

and on the DL380G4 running 2.6.24:
---------------------------------------------------------
[root@lpsdm52 ~]# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
hpet acpi_pm jiffies tsc
[root@lpsdm52 ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
hpet

Cheers
Martin