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CPU is higher than expected on idle NVMe SAN systems

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ontap-9
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perf
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Applies to

  • ONTAP 9
  • Cloud Volumes ONTAP
  • All FAS/AFF systems
  • Amazon FSx for NetApp ONTAP
  • ONTAP Select
  • All frontend SAN NVMe protocols, such as NVMe-oF or NVMe/TCP

Issue

  • CPU may idle around 10% or 20% when clients are connected but there are 0 client IOPs
  • Example: sysstat -m at node shell from A400 shows cores 0-14 at 0%, but 15-19 at 40% (some rows removed for readability):
Cluster::> node run -node <node> sysstat -m 1
CPU15 CPU16 CPU17 CPU18 CPU19
  44%   38%   39%   41%   38%
  44%   37%   40%   42%   38%
  45%   38%   39%   44%   38%
  43%   37%   40%   41%   38%
  44%   37%   39%   41%   38%
  45%   45%   52%   46%   42%
  43%   37%   39%   42%   38%
  44%   38%   39%   40%   38%
  44%   41%   40%   41%   38%
  44%   38%   38%   41%   38%

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