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What are CPU as a compute resource and the CPU domains in ONTAP 9?

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Applies to

  • ONTAP 9

Answer

  • ONTAP uses a Coarse Symmetric Multiprocessing (CSMP) design which partitions system functions into logical processing domains.
  • Each logical processing domain has a set of rules that govern how and when the logical CSMP domain can be scheduled across physical CPU cores.
  • These rules are designed to ensure that all processing occurs in a safe and efficient manner.

  • The following table describes some of the common logical processing domains, their typical tasks.
  • It also describes if the logical domain can run on one or more CPU cores concurrently, along with any specific scheduling rules:

Domain name

Typical Tasks in Domain

CPU Concurrency

Notes

nwk_exclusive

IP processing, NFS protocol processing

1

Networking code which can only run on a single CPU concurrently

nwk_exempt

IP processing, NFS protocol processing, SMB processing

1+

Maximum number of CPUs is dependent on controller model and ONTAP release

nwk_legacy (pre 9.2)

network (9.2+)

IP processing, NFS protocol processing

1

Networking code which can only run on a single CPU concurrently

storage

SCSI communication
with disks

1+

Concurrency of 1 if less than 6 CPUs

raid

RAID subsystem

1

 

raid_exempt

RAID subsystem

1+

XOR_Ex

RAID subsystem XOR parity processing

1+

ssan_exempt

SCSI (FCP/iSCSI) processing

1+

Kahuna

Serialized WAFL and anything not in another domain

1

Exclusive with WAFL_Ex (i.e. either Kahuna can be active on 1 CPU or WAFL_Ex can be active on 1+ CPUs, but both cannot be active at the same time)

WAFL_Ex

Parallelized WAFL

1+

Exclusive with Kahuna (i.e. either Kahuna can be active on 1 CPU or WAFL_Ex can be active on 1+ CPUs, but both cannot be active at the same time)

WAFL_MPClean

WAFL

1+

 

SM_Exempt

SnapMirror

1+

 

exempt

General parallelized work

1+

 

hostOS

Tasks owned by the BSD layer including NTP, environmental sensor monitoring, ZAPI handling, autosupport

1+

 
reserved Reserved based on system performance and capacity requirements.    

 

  • Logical CSMP domains are scheduled to run on physical CPU cores by the ONTAP kernel.
  • The scheduling logic is unique to a given ONTAP release and hardware platform and is tuned to maximize the overall system performance.
  • The level of parallelism seen for a given logical domain varies based on a number of factors, including:
    • Incoming workload rate
    • Type of work being requested
    • ONTAP OS version and more.

Additional Information

Scheduling behaviors:
  • Pinning of heavily used logical domains to physical CPU core to maximize cache efficiency.
  • Shutdown of physical CPU cores at various load points to optimize processing of the run queue.
  • These optimizations might appear to result in an uneven balancing of workload across physical CPU cores.
  • This behavior is by design and is optimized for each specific ONTAP release and platform combination.
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