linux-kernel - Re: IRQ splitting

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Message-ID: <20070405122341.482f5e26@freekitty>
Date:	Thu, 5 Apr 2007 12:23:41 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	linux-kernel@...r.kernel.org
Subject: Re: IRQ splitting

On Thu, 05 Apr 2007 08:34:59 -0600
Robert Hancock <hancockr@...w.ca> wrote:

> Jan Engelhardt wrote:
> > Hello list,
> > 
> > 
> > 
> > let's take the following /proc/interrupts dump (CPU2,CPU3 trimmed)...
> > 
> >            CPU0       CPU1
> >   0:   37041766   37038991  IO-APIC-edge  timer
> >   1:         10          2  IO-APIC-edge  i8042
> >   8:          0          0  IO-APIC-edge  rtc
> >   9:          0          0  IO-APIC-level  acpi
> >  12:        114          0  IO-APIC-edge  i8042
> >  14:      25219    5800049  IO-APIC-edge  ide0
> > 201:     260381     238454  IO-APIC-level  aacraid
> > 209:          0          0  IO-APIC-level  ohci_hcd:usb1
> > 217:          0          0  IO-APIC-level  ehci_hcd:usb2
> > 225:   57531742          0  IO-APIC-level  eth0,radeon@pci:0000:03:00.0
> > 233:         26          0  IO-APIC-level  eth1
> > NMI:       1661       1397
> > LOC:  147579966  147579949
> > ERR:          0
> > MIS:          0
> > 
> > My question is whether it is possible that eth0's interrupts go to CPU0
> > and radeon's to CPU1, and if so, how I would enable that. Alternatively,
> > is it possible to just move eth0 or radeon to a different interrupt?
> 
> Generally (at least in APIC mode) the IRQ assignments are based on 
> hard-wired interrupt lines on the board. In this case, the slots that 
> the Radeon and eth0 card are in likely share a physical interrupt line 
> and there is no way to separate them in software. You can try moving the 
>   card(s) to different slots..
> 

If the radeon and/or the Ethernet driver support MSI, that would split
out the IRQ's as well.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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