[mythtv-users] OT? /proc/pci

[Tim Tait]

Jason Kraftcheck wrote:

>Joel Anderson wrote:
>  
>
>>Marc-David Meijer wrote:
>>
>>As I understand it, PCI devices don't depend on IRQs anyway.  They use
>>interrupt "channels", and IRQs are just kept around to keep legacy stuff
>>happy.  You will often see many devices appear to "share" the same IRQ,
>>but it is not really true since IRQ's can't really _be_ shared.
>>
>>Someone please comment if I haven't explained this correctly.  It's a
>>simplification, but it basically means that IRQ issues shouldn't come
>>into play unless you have some legacy hardware in the system also.
>>    
>>
>
>I'm no expert either, but I think they are actually "shared".  The
>interrupt handler must poll each device by invoking the interrupt
>handler in the driver for each device sharing the interrupt.  Thus
>there's a slight performance loss when sharing interrupts, and also the
>possibility for buggy drivers to interfere with each other.
>  
>
Newer PCI devices support "Message Signalled Interrupts" which use no 
physical IRQ line, but instead write a pre-configured value to the PCI 
bridge inbound MSI register to cause a unique interrupt. I can't say for 
sure the 250MCE actually does that (or that the driver sets it up that 
way) but it is possible.  People have commented eslwhere on the list 
that it appears the 250MCE needs a PCI Rev 2.2 compliant motherboard, so 
you might want to check your  mobo docs out and see if it complies.

Tim

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