[LAU] midi triggering delay

[andy baxter]

James Cameron wrote:
> On Tue, Sep 08, 2009 at 07:17:30PM -1000, david wrote:
>   
>> USB not sharing interrupts with anything?
>>     
>
> Andy's original post contained /proc/interrupts which showed some
> sharing was happening.  Here's a cut:
>
>  16:     380396     233180   IO-APIC-fasteoi   uhci_hcd:usb4, yenta
>  17:     829711     532117   IO-APIC-fasteoi   uhci_hcd:usb5, ohci1394, HDA Intel
>  18:          0          0   IO-APIC-fasteoi   mmc0
>  19:          2          0   IO-APIC-fasteoi   ehci_hcd:usb6
>  20:         18         17   IO-APIC-fasteoi   uhci_hcd:usb1
>  21:          0          0   IO-APIC-fasteoi   uhci_hcd:usb2
>  22:     305246     302929   IO-APIC-fasteoi   ehci_hcd:usb3
>
> Sharing interrupts adds a tiny delay to interrupt handling; if this has
> truly become significant, there's a design issue somewhere else.
>
> (Shared interrupts with modern kernels are not a huge problem, since the
> drivers check to see if the interrupt they have is legitimate before the
> kernel chains on to the next driver.  It's the waste of that additional
> check that people want to avoid.)
>
>   
The usb port I'm using is on INT 21 (uhci_hcd:usb2), which doesn't share 
with anything.

andy