Public bug reported:

[Impact]
Transmit packet steering (xps) settings don't work when
the number of queues (cpus) is higher than 64. This is
currently still an issue on the 4.15 kernel (Xenial -hwe
and Bionic kernels). 

It was fixed in Intel's i40e driver version 2.7.11 and
in 4.16-rc1 mainline Linux (i.e. Cosmic, Disco have fix).

Fix
-----
The following commit fixes this issue (as identified
by Lihong Yang in discussion with Intel i40e team):

"i40e: Fix the number of queues available to be mapped for use"
Commit: bc6d33c8d93f5999920e97a8c6330b8910053d4f


[Test Case]
1. Kernel version: Bionic/Xenial -hwe: any 4.15 kernel
   i40e driver version: 2.1.14-k 
   Any system with > 64 CPUs

2. For any queue 0 - 63, you can read/set tx xps:
   
echo ffffffff > /sys/class/net/eth2/queues/tx-63/xps_cpus
echo $?
0
cat /sys/class/net/eth2/queues/tx-63/xps_cpus
00,00000000,ffffffff 

  But for any queue number > 63, we see this error:

echo ffffffff > /sys/class/net/eth2/queues/tx-64/xps_cpus
echo: write error: Invalid argument

cat /sys/class/net/eth2/queues/tx-64/xps_cpus
cat: /sys/class/net/eth2/queues/tx-64/xps_cpus: Invalid argument

** Affects: linux (Ubuntu)
     Importance: High
         Status: Confirmed

** Affects: linux (Ubuntu Bionic)
     Importance: High
     Assignee: Nivedita Singhvi (niveditasinghvi)
         Status: Confirmed


** Tags: bionic

** Also affects: linux (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu)
       Status: New => Confirmed

** Changed in: linux (Ubuntu Bionic)
       Status: New => Confirmed

** Changed in: linux (Ubuntu)
   Importance: Undecided => High

** Changed in: linux (Ubuntu Bionic)
   Importance: Undecided => High

** Changed in: linux (Ubuntu Bionic)
     Assignee: (unassigned) => Nivedita Singhvi (niveditasinghvi)

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https://bugs.launchpad.net/bugs/1820948

Title:
  i40e xps management broken when > 64 queues/cpus

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