[openib-general] IRQ sharing on PCIe bus

[Michael Krause]

At 02:05 PM 10/10/2005, Roland Dreier wrote:
>     Roland> BTW, for "INTx emulation" on PCI Express, there are no
>     Roland> physical interrupt lines -- interrupts are asserted and
>     Roland> deasserted with messages.  So PCI Express interrupts are
>     Roland> unshared.
>
>     Michael> They are messages upstream that any device.

                                                      ^ sent

Sorry.  Insert "sent" above.

>That doesn't parse for me.  Was what I said wrong?

No.  Just clarifying that they are not unique per device.  INTx being a 
message does not change the fundamental semantics of a "wire" being 
asserted.  Hence, if the wire was shared before, then there is no reason 
why this would not be the same with PCIe sans.  It really is an OS issue as 
to how INTx interrupts are assigned to different processors and to what 
extent then end up being shared.  The host bridge can play some tricks as 
well as you noted.  Again, the goal within the PCI-SIG is to move people to 
MSI-X and to eliminate INTx long-term.  In fact, one area under development 
is asking the SIG's members whether INTx can be eliminated entirely which 
would go a long ways to simplifying designs both in hardware and software.

Mike 
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