CPU as a compute resource
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 |
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.