[E1000-devel] ixgbe: MSI-X on uniprocessors, interrupt throttling

[Julian S. <jst...@os...>]

Hello,

looking at the ixgbe source in Linux 3.3.3 it seems that MSI-X is never
enabled on uniprocessors.

In ixgbe_set_interrupt_capability, it calculates the v_budget (vector
budget) as  min(...,(int)num_online_cpus()) + NON_Q_VECTORS), which
results in 2 (1 online CPU + NON_Q_VECTORS (1)).

Later in ixgbe_acquire_msix_vectors we check if the vector budget is at
least MIN_MSIX_COUNT (3), fail and fallback to MSI mode. The question is
whether this is intended.

I noticed this, because interrupt throttling seems to have no effect in
MSI mode or at least I am unable to limit interrupt rate using the
relevant module flags or ethtool. Can anyone comment on this?

Regards, Julian