linux-kernel - Re: cpufreq longhaul locks up

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Message-ID: <Pine.LNX.4.61.0705061125010.8623@yvahk01.tjqt.qr>
Date:	Sun, 6 May 2007 11:32:24 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Rafał Bilski <rafalbilski@...eria.pl>
cc:	Wander Winkelhorst <w.winkelhorst@...il.com>,
	David Johnson <dj@...id-web.co.uk>,
	linux-kernel@...r.kernel.org, cpufreq@...ts.linux.org.uk
Subject: Re: cpufreq longhaul locks up


On May 6 2007 11:23, Rafał Bilski wrote:
>
>> <6>No local APIC present or hardware disabled
>> <7>mapped APIC to ffffd000 (011ea000)
>> <5>Local APIC not detected. Using dummy APIC emulation.
>
>I/O APIC is very bad thing with Longhaul, but You don't have 
>local APIC, so it shouldn't be used.
>
>> <6>ACPI: Using PIC for interrupt routing
>
>Looks like it isn't.
>
>> <4>ACPI: PCI Interrupt Link [ALKA] (IRQs *20), disabled.
>> <4>ACPI: PCI Interrupt Link [ALKB] (IRQs *21)
>> <4>ACPI: PCI Interrupt Link [ALKC] (IRQs *22)
>> <4>ACPI: PCI Interrupt Link [ALKD] (IRQs *23), disabled.
>
>This is pointing to I/O APIC, but I don't see later that 
>such high interrupts are used. And if I/O APIC would be in 
>use You would have lockup in the moment of transition.

cn:~ # cat /proc/interrupts 
           CPU0       
  0:    1745595    XT-PIC-XT        timer
  1:         29    XT-PIC-XT        i8042
  2:          0    XT-PIC-XT        cascade
  5:       1194    XT-PIC-XT        uhci_hcd:usb1, uhci_hcd:usb2, eth0
  7:          1    XT-PIC-XT        ehci_hcd:usb5
  8:          2    XT-PIC-XT        rtc
  9:          0    XT-PIC-XT        acpi
 12:          0    XT-PIC-XT        uhci_hcd:usb3, uhci_hcd:usb4, eth1
 14:      59882    XT-PIC-XT        libata
 15:          0    XT-PIC-XT        libata
NMI:          0 
LOC:          0 
ERR:          0
MIS:          0

So, just the regular 16.

>I was suspecting:
>> One of the 2.6.21 regressions was Guilherme's problem seeing his box
>> lock up when the system detected an unstable TSC and dropped back to
>> using the HPET.
>> 
>> In digging deeper, we found the HPET is not actually incrementing on
>> this system. And in fact, the reason why this issue just cropped up was
>> because of Thomas's clocksource watchdog code was comparing the TSC to
>> the HPET (which wasn't moving) and thought the TSC was broken.
>
>because I know that VT8237 has HPET built in. But I don't see any lines 
>starting with "hpet: enabled" or something similar. But I don't know 
>what to search for. I didn't have contact with HPET earlier.
>It is very similar and Your problem with ondemand is starting right 
>after
>
>> May  3 19:17:22 cn kernel: Clocksource tsc unstable (delta = -136422685 
>> ns)
>
>I don't see such message as long as "performance" governor is used. 

Well this message pops up whenever the frequency changes, because
the CPU does not have constant_tsc. E.g.

<performance is default and active>
echo 598000 >/sys/devices/cpu/cpu0/cpufreq

spews out the clocksource message. I do not think the clocksource
is a culprit. The kernel just noticed the TSC jumped and hence
uses a new clocksource.

>Anyway adding "hpet=disable" at boot should confirm for sure that it 
>isn't it. And I think that John already ruled this out by 
>clocksource=acpi_pm.
>
>Sorry 
>Rafał

Nevermind, it does not look like it gets any cooler at lower frequencies,
so it's a nobrainer to run it at the default 733.


Jan
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