Re: Pin-pointing the root of unusual application latencies

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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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