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CPU as a compute resource

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clustered-data-ontap-8
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Applies to

  • ONTAP 9
  • Clustered Data ONTAP 8 
  • Data ONTAP 8 7-Mode 
  • Data ONTAP 7 and earlier 

Answer

  • Data 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 (7-mode and cDOT), SMB processing (cDOT)

1+

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

nwk_legacy

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 prior to Data ONTAP 8.2.1 or if less than 6 CPUs

raid

RAID subsystem

1

 

raid_exempt

RAID subsystem

1+

Introduced in Data ONTAP 8.2

XOR_Ex

RAID subsystem XOR parity processing

1+

Introduced in ONTAP 9.0

target

SCSI (FCP/iSCSI) processing

1

 7-mode only

ssan_exempt

SCSI (FCP/iSCSI) processing

1+

Introduced in clustered Data ONTAP 8.2

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_XCleaner

WAFL

1+

 

SM_Exempt

SnapMirror

1+

 

cifs

SMB protocol processing (7-mode only)

1

Initial decoding only; majority of SMB processing occurs in WAFL

exempt

General parallelized work

1+

 

hostOS

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

1+

 

 

  • Logical CSMP domains are scheduled to run on physical CPU cores by the Data ONTAP kernel.
  • The scheduling logic is unique to a given Data 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
    • Data 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 Data ONTAP release and platform combination.