chcpumf - Set limits for the CPU measurement sampling facility buffer

6.10 LPAR mode

Use the chcpumf command to set limits for the CPU measurement sampling facility buffer.

The sampling facility is designed for autonomous buffer management, and you do not usually need to intervene. However, you might want to change the minimum or maximum size, for example, for one of the following reasons:
  • There are considerable resource constraints on your system, and the sampling facility stops because it tries to allocate more buffer space than is available.
  • As an expert user of perf and the sampling facility, you want to explore results with particular buffer settings.

chcpumf syntax

Read syntax diagramSkip visual syntax diagramchcpumf -V -m  <min_sdb>-x  <max_sdb>
where:
-m <min_sdb> or --min <min_sdb>
specifies the minimum sampling facility buffer size in sample-data-blocks. A sample-data-block occupies approximately 4 KB. The sampling facility starts with this buffer size if it exceeds the initial buffer size that is calculated by the sampling facility.
-x <max_sdb> or --max <max_sdb>
specifies the maximum sampling facility buffer size in sample-data-blocks. A sample-data-block occupies approximately 4 KB. While it is running, the sampling facility dynamically adjusts the buffer size to a suitable value, but cannot exceed this limit.
-V or --verbose
displays the buffer size settings after the changes.
-v or --version
displays the version number of chcpumf and exits.
-h or --help
displays out a short help text, then exits. To view the man page, enter man chcpumf.

Example

To change the minimum buffer size to 500 times the size of a sample-data-block and the maximum buffer size to 1000 times the size of a sample-data-block, issue: 
# chcpumf -V -m 500 -x 1000
Sampling buffer sizes:
    Minimum:    500 sample-data-blocks
    Maximum:   1000 sample-data-blocks