tree b4bcb66ccdeb56bb2db13c7fca4a6f84d12aa67e
parent 4b732cd4bb6006ad7fd4d5cdba27fcb751cdf4b7
author Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com> 1467040603 -0300
committer Jeff Kirsher <jeffrey.t.kirsher@intel.com> 1468564752 -0700

i40e: use valid online CPU on q_vector initialization

Currently, the q_vector initialization routine sets the affinity_mask
of a q_vector based on v_idx value. Meaning a loop iterates on v_idx,
which is an incremental value, and the cpumask is created based on
this value.

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 incremental filling in q_vector cpumask might
lead to multiple offline CPUs being assigned to q_vectors.

Example: if we have a system with 8 cores each one containing 8 logical
CPUs (SMT == 8 in this case), we have 64 CPUs in total. But if SMT is
disabled, only the 1st CPU in each core remains online, so the
cpu_online_mask in this case would have only 8 bits set, in a sparse way.

In general case, when SMT is off the cpu_online_mask has only C bits set:
0, 1*N, 2*N, ..., C*(N-1)  where
C == # of cores;
N == # of logical CPUs per core.
In our example, only bits 0, 8, 16, 24, 32, 40, 48, 56 would be set.

This patch changes the way q_vector's affinity_mask is created: it iterates
on v_idx, but consumes the CPU index from the cpu_online_mask instead of
just using the v_idx incremental value.

No functional changes were introduced.

Signed-off-by: Guilherme G Piccoli <gpiccoli@linux.vnet.ibm.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>