linux-kernel - RE: timer interrupt stucks using tickless kernel

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Date:	Tue, 8 Dec 2009 01:33:12 +0000
From:	"Ioannis Kyriakopoulos" <johnkyr83@...mail.com>
To:	"'john stultz'" <johnstul@...ibm.com>
CC:	<linux-kernel@...r.kernel.org>
Subject: RE: timer interrupt stucks using tickless kernel

Thanks for the valuable help so far.

>> 2.	When performing cat proc/interrupts, I see that:
>>           0:        157   IO-APIC-edge      timer
>> 	How the system timer is attached on IO-APIC at the time that the
>> IO-APIC 
>>       is disabled on kernel configurations? Basically, the timer is not the
>> only
>>       peripheral attached to IO-APIC as can be seen by /proc/interrupts.
>> 
>> Here is the output of /proc/interrupts :
>> 
>>            CPU0
>>   0:        157   IO-APIC-edge      timer
>>   1:          2   IO-APIC-edge      i8042
>>   4:        544   IO-APIC-edge      serial
>>   8:          1   IO-APIC-edge      rtc0
>>   9:          0   IO-APIC-fasteoi   acpi
>>  12:          4   IO-APIC-edge      i8042
>>  14:          4   IO-APIC-edge      ata_piix
>>  15:          0   IO-APIC-edge      ata_piix
>>  16:          0   IO-APIC-fasteoi   uhci_hcd:usb5
>>  18:          0   IO-APIC-fasteoi   uhci_hcd:usb4
>>  19:         45   IO-APIC-fasteoi   ata_piix, uhci_hcd:usb3
>>  22:        149   IO-APIC-fasteoi   HDA Intel
>>  23:         72   IO-APIC-fasteoi   ehci_hcd:usb1, uhci_hcd:usb2
>>  27:          0   PCI-MSI-edge      eth0
>> NMI:          0   Non-maskable interrupts
>> LOC:    1865130   Local timer interrupts
>            ^^^
>This value should be incrementing at HZ freq.

Are you sure about that? ASAIK the Local timer interrupts (generated 
by the LAPIC timer) are only used for timekeeping. The system tick is 
generated by IRQ0 which in my second configuration should be triggered 
by HPET (because I have enabled the HPET timer support). Also, if the 
interrupts generated by LAPIC are incremented at HZ freq, why the 
interrupts generated by the timer (IRQ0) not happen at the same frequency
 as well? 

Furthermore, we don't have an answer on why IO-APIC is used at the time
that it is disabled on kernel configurations. The fact that I have enabled
LAPIC timer support doesn't justify the use of the IO-APIC controller 
by each own.

>Is there something your actually having problems with here? Ignoring
>which interrupt line is used for the timer event, the system is
>functioning properly, right?

Yes, apart from that, everything is working OK but it's really important
for me to get an answer on these issues.

Kind Regards,

John K.

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