Re: What determines which interrupts are shared under Linux?

From: Sergei Shtylyov
Date: Tue Aug 15 2006 - 10:27:17 EST


Roger Heflin wrote:

On Linux when interrupts are defined similar to below, what defines say
ide2, ide3 to be on the same interrupt? The bios, linux, the driver using the interrupt?

In this particular case (I suppoer both belong to the same IDE conrtoller) the hardware design determines this in part and software in another part.
If the PCI IDE controller was in the leagcy mode (it should be ide0/1 then), the interrupts would've been 14 and 15. But in the native PCI mode, both chanels share the same interrupt level (if they're both in native mode that is).

And can that be controlled/overrode at the kernel/driver level?

The only possibility might be do disable ide0/1 in the BIOS I guess.

I have identified that the disks that are shared on ide2, ide3 do funny
things when both are being heavily used (dma_expiry), this is an older driver versions
but I have experienced it before with a lot newer driver, and a bios adjustment
previously fixed a similar issue, so that may be what is needed in this case also,
I am not sure how they fixed it, but I suspect that the setup the interrupt
to not be shared.

I doubt that your suspicions are justified.

I have a large number of machines and under heavy loads all
seem to duplicate the issue, and it always happens with the disks on ide2/ide3,
never on the disk connected to ide4.

BTW, you never named your particular IDE hardware.

0: 56616921 5359998 7002142 938817 XT-PIC timer
1: 8 88 96 0 IO-APIC-edge i8042
2: 0 0 0 0 XT-PIC cascade
4: 2091 100 208 2477 IO-APIC-edge serial
8: 0 0 0 0 IO-APIC-edge rtc
9: 0 0 0 0 IO-APIC-level acpi
20: 0 0 0 0 IO-APIC-level ehci_hcd
21: 0 950 401419 414482 IO-APIC-level ide4, ohci_hcd
22: 1165 1704243 576247 6796 IO-APIC-level ide2, ide3
47: 65971 0 0 0 IO-APIC-level eth0
NMI: 1 1 1 1
LOC: 69904264 69877733 69879541 69901903
ERR: 0
MIS: 105

MBR, Sergei
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