Too many devices using IRQ10?

[Peter Arremann]

On Monday 14 November 2005 01:47, Steffen Kluge wrote:
> Hi all,
> I've got this niggling problem that I revisit every time a new kernel is
> released for FC4, however, it doesn't appear to change:
>
> On my notebook it seems that by default most devices are sharing IRQ10,
> including the ones I would normally associate with performance (disk,
> net):
>
> $ cat /proc/interrupts
>            CPU0
>   0:      34756          XT-PIC  timer
>   1:         91          XT-PIC  i8042
>   2:          0          XT-PIC  cascade
>   8:          1          XT-PIC  rtc
>   9:       1138          XT-PIC  acpi
>  10:      10853          XT-PIC  libata, ipw2200, Intel ICH6,
> ehci_hcd:usb1, uhci_hcd:usb2, uhci_hcd:usb3, uhci_hcd:usb4, uhci_hcd:usb5,
> yenta, ohci1394, eth0 12:        814          XT-PIC  i8042
>  14:        454          XT-PIC  ide0
> NMI:          0
> ERR:          0
>
> The interrupts are assigned by ACPI. Since I need ACPI for cpuspeed I
> don't want to disable it altogether, but instead fiddled with boot
> parameters to keep it from doing the IRQ assignment. For example, my
> current boot command line contains "pci=noacpi,routeirq", which seems to
> improve the situation:
>
> $ cat /proc/interrupts
>            CPU0
>   0:      54122          XT-PIC  timer
>   1:         73          XT-PIC  i8042
>   2:          0          XT-PIC  cascade
>   5:        399          XT-PIC  uhci_hcd:usb3, ohci1394, eth0
>   7:          2          XT-PIC  ehci_hcd:usb1, uhci_hcd:usb2
>   8:          1          XT-PIC  rtc
>   9:       1727          XT-PIC  acpi
>  10:         41          XT-PIC  ipw2200, Intel ICH6, uhci_hcd:usb4, yenta
>  11:      10615          XT-PIC  libata, uhci_hcd:usb5
>  12:        118          XT-PIC  i8042
>  14:        610          XT-PIC  ide0
> NMI:          0
> ERR:          0
>
> With this, the interrupts are much more evenly used.
>
> Now, I guess my question is, does this even matter? Is sharing a single
> IRQ among many devices a potential performance issue? Am I losing
> anything by stopping ACPI from messing with IRQ's?
>
> Cheers
> Steffen.

The issue you're seeing is actually more common than you think - Especially on 
laptops. Most ACPI implementations still suck - many people say that before 
you could learn writing good DTSDs ACPI will be outdated ;) 

Seriously though - I ran into a very similar scenario on some HP desktops 
fairly recently and running a gigabit lan, I saw about 4% performance drop 
when completely saturation the network with ftp accesses. That's the result 
of disks and ethernet competing. For each interrupt the system needs to query 
each device if it caused the interrupt. 

For your laptop (slower disk) its probably even less. My current laptop looks 
like this:

 11:    5409254          XT-PIC  Intel 82801DB-ICH4, Intel 82801DB-ICH4 Modem, 
ehci_hcd, uhci_hcd, uhci_hcd, uhci_hcd, yenta, ath0, nvidia

and I've never seen any issues. If you really care about it, try update your 
bios or  search the web for a better DSDT. Other than that, I'd not worry. 
NoACPI will btw, seriously decrease your battery lifetime and on most laptops 
I've seen cause fan trigger/speed issues. 

Peter.