Re: mlx4_core unable to use MSI-x on our nodes

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Thu, Jul 22, 2010 at 10:56:55AM -0700, Meyer, Donald J wrote:

> In our dmesg log I see "mlx4_core 0000:02:00.0: Only 12 MSI-X
> vectors available, need 25. Not using MSI-X" which if I read it
> correctly says our mlx4_core is unable to use MSI-X which if I also
> understand correctly means the mlx4_core can't use the sharing of
> interrupts among all processors.
 
> If this is correct, do we want to try to fix this so the mlx4_core
> can use MSI-X and share the interrupts?
 
Yes, you will get better performance with MSI-X, fixing it is
worthwhile..

> And if we do want to fix this, do you have any suggestions for how
> to fix it?

AFAIK, the only way to fix this is to user a newer kernel (or
different build options?).. Some kernels do not provide very many
interrupt vectors so they get exhausted easily.

Ie the 2.6.28 kernel I have here is using vector numbers 2298 for MSI
vectors.. There are lots of interrupts available :)

Jason
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