Re: RFC: MSI/MSI-X implementation

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Thu, Nov 13, 2014 at 01:59:09PM -0600, David Young wrote:
> On Thu, Nov 13, 2014 at 12:41:38PM +0900, Kengo NAKAHARA wrote:
> > (2014/11/13 11:54), David Young wrote:
> > >On Fri, Nov 07, 2014 at 04:41:55PM +0900, Kengo NAKAHARA wrote:
> > >>Could you comment the specification and implementation?
> > >
> > >The user should not be on the hook to set processor affinity for the
> > >interrupts.  That is more properly the responsibility of the designer
> > >and OS.
> > 
> > I wrote unclear explanation..., so please let me redescribe.
> > 
> > This MSI/MSI-X API *design* is independent from processor affinity.
> > The device dirvers can use MSI/MSI-X and processor affinity
> > independently of each other. In other words, legacy interrupts and
> > INTx interrupts can use processor affinity still. Furthermore,
> > MSI/MSI-X may or may not use processor affinity.
> 
> MSI/MSI-X is not half as useful as it ought to be if a driver's author
> cannot spread interrupt workload across the available CPUs.  If you
> don't mind, please share your processor affinity proposal and show how
> it works with interrupts.

Nevertheless, I would prefer to see it getting into the tree first.
While manual load balancing by the administrator is often suboptimal,
there are situations where it is certainly desirable. As such, I believe
that the logic for higher intelligence in the default can be added as a
second step.

Joerg