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SubjectRe: Pin-pointing the root of unusual application latencies
John Sigler wrote:

> Len Brown wrote:
>
>> John Sigler wrote:
>>
>>> # cat /proc/interrupts
>>> CPU0
>>> 0: 37 XT-PIC-XT timer
>>> 1: 2 XT-PIC-XT i8042
>>> 2: 0 XT-PIC-XT cascade
>>> 7: 0 XT-PIC-XT acpi
>>> 10: 175 XT-PIC-XT eth2, Dta1xx
>>> 11: 1129 XT-PIC-XT eth0
>>> 12: 4 XT-PIC-XT eth1
>>> 14: 21482 XT-PIC-XT ide0
>>> NMI: 0
>>> LOC: 161632
>>> ERR: 0
>>> MIS: 0
>>>
>>> IRQ 10 is shared between a NIC and an I/O board.
>>>
>>> For eth2, the kernel said:
>>> ACPI: PCI Interrupt 0000:00:0a.0[A] -> Link [LNKC]
>>> -> GSI 10 (level, low) -> IRQ 10
>>>
>>> For Dta1xx, the kernel said:
>>> ACPI: PCI Interrupt 0000:02:0e.0[A] -> Link [LNKC]
>>> -> GSI 10 (level, low) -> IRQ 10
>>>
>>> Is it possible to avoid the two boards sharing IRQ 10?
>>
>> Maybe. In this configuration, INTA of the two devices
>> is physically connected to the same wire on the device-side
>> of the interrupt re-mapper -- so you'd have to change the configuration.
>> If you have an IOAPIC and can enable it, that will not hurt --
>
> I believe this board does not provide an IO-APIC.
> Even the LAPIC is disabled in the BIOS.
> (Why would they do that??)
>
>> though unless something else changes, these devices are still
>> tied together on the device-side of the mapper.
>> So if you can physically move one of the devices to another slot
>> that is your best bet.

The NICs are on-board, therefore it is not possible to move them.

The motherboard only has one PCI slot, so the manufacturer includes
a backplane (is that what it's called?) to provide two PCI slots.

The results I've given so far were with the I/O board inserted in
the bottom slot. If it is inserted in the top slot, the results are
different indeed.

# cat /proc/interrupts
CPU0
0: 37 XT-PIC-XT timer
1: 2 XT-PIC-XT i8042
2: 0 XT-PIC-XT cascade
5: 20270 XT-PIC-XT Dta1xx
7: 0 XT-PIC-XT acpi
10: 4 XT-PIC-XT eth2
11: 2639 XT-PIC-XT eth0
12: 4 XT-PIC-XT eth1
14: 13984 XT-PIC-XT ide0
NMI: 0
LOC: 518501
ERR: 0
MIS: 0

$ diff dmesg.adlink dmesg2.adlink
208c208,210
< ACPI: PCI Interrupt 0000:02:0e.0[A] -> Link [LNKC] -> GSI 10 (level,
low) -> IRQ 10
---
> ACPI: PCI Interrupt Link [LNKD] enabled at IRQ 5
> PCI: setting IRQ 5 as level-triggered
> ACPI: PCI Interrupt 0000:02:0f.0[A] -> Link [LNKD] -> GSI 5 (level,
low) -> IRQ 5

$ diff lspci.adlink lspci2.adlink
121c121
< 02:0e.0 Multimedia controller: PLX Technology, Inc. 9056 PCI I/O
Accelerator
---
> 02:0f.0 Multimedia controller: PLX Technology, Inc. 9056 PCI I/O
Accelerator
126c126
< Interrupt: pin A routed to IRQ 10
---
> Interrupt: pin A routed to IRQ 5

I'll give a 4-port PCI NIC a spin.

Regards.
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