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We have an issue with the i40e driver, present in kernels pre-4.8, like
Xenial v4.4 (from Ubuntu 16.04.1).

i40e driver has an issue in interrupt vector assignment in case of
sparse CPU masks, like when some CPUs are disabled. The driver does a
linear mapping not taking gaps on cpumask into account. This is a
problem in systems with multiple logical CPUs per core (like in SMT
scenarios).

If we disable some logical CPUs, by turning SMT off for example, we will
end up with a sparse cpu_online_mask, i.e., only the first CPU in a core
is online, and the incremental/linear filling in the interrupt cpumask
might lead to multiple offline CPUs being assigned to the struct
q_vector in the driver, leading to issues when interrupts are requested,
like the following message in PowerPC systems:


[141.97] ics_opal_set_affinity: No online cpus in the mask 
00200000,00000000,00000000,00000000 for irq 302


This message is output of interrupt controller in Power systems, a complain 
that the cpumask does not make sense to that particular system.

** Affects: linux (Ubuntu)
     Importance: Undecided
     Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
         Status: New


** Tags: architecture-ppc64le bugnameltc-145954 severity-high 
targetmilestone-inin16041
-- 
ISST-LTE: Briggs:Stratton:UbuntuKVM:  ics_opal_set_affinity on host kernel log 
using Intel X710 (i40e driver)
https://bugs.launchpad.net/bugs/1703663
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