Improvements to MSI-X API

Improvements to MSI-X API

[Benjamin Herrenschmidt]

Hi folks !

A while back, Matthew was mentioning (iirc) some work on improving the
MSI-X APIs to be a bit less inflexible, for example by allowing setting
up individual MSI-X interrupts independently at runtime.

Is that still something being worked on ?

Another thing I've got poked about by some folks working on a new
adapter is that they would like the ability to control aliasing if we
cannot provide all the MSI-X. IE. IF the adapter has 16 sources but we
can only provide 10, they want the driver to be able to enable all 16,
but configure some of them to shoot the same message to the same
address.

This is useful in the case where the sources aren't really separate
queues but totally different type of messages, to be able to do some
fine grained control of what goes where, as the HW doesn't do that sort
of aliasing itself.

Cheers,
Ben.

Re: Improvements to MSI-X API

[Benjamin Herrenschmidt]

On Tue, 2012-09-11 at 13:47 +1000, Benjamin Herrenschmidt wrote:
> Hi folks !
> 
> A while back, Matthew was mentioning (iirc) some work on improving the
> MSI-X APIs to be a bit less inflexible, for example by allowing setting
> up individual MSI-X interrupts independently at runtime.
> 
> Is that still something being worked on ?
> 
> Another thing I've got poked about by some folks working on a new
> adapter is that they would like the ability to control aliasing if we
> cannot provide all the MSI-X. IE. IF the adapter has 16 sources but we
> can only provide 10, they want the driver to be able to enable all 16,
> but configure some of them to shoot the same message to the same
> address.
> 
> This is useful in the case where the sources aren't really separate
> queues but totally different type of messages, to be able to do some
> fine grained control of what goes where, as the HW doesn't do that sort
> of aliasing itself.

Note that a way to avoid problems with existing kernels & APIs might be
in HW to:

 - Have a "mandatory" interrupt (MSI-X entry 0 ?)
 - Have the HW route any unconfigured source to that interrupt

IE. Enforce the aliasing.

Cheers,
Ben.