Before you begin
Ensure that your workload is configured to request compression level 1. For software that is
hardcoded to request a level other than 1, use the techniques that are described in Overriding the defaults to force compression with the on-chip accelerator.
Procedure
- Confirm by comparison.
Run the same workload twice: once with the on-chip accelerator enabled and once with the on-chip
accelerator off. Compare the results to assess the effect of the on-chip accelerator.
By default, the on-chip accelerator is enabled for workloads in both user space and the kernel.
Use the applicable control to turn off the on-chip accelerator for the reference run:
- User space
- Set the environment variable DFLTCC to 0.
- Kernel
- Restart Linux® with the kernel parameter setting
dfltcc=off.
- Confirm through hardware counters.
Evaluate hardware counters to directly confirm that the on-chip accelerator is active. For
example, you can evaluate the counters with the following symbolic names:
- DFLT_ACCESS
- Cycles CPU spent obtaining access to Deflate unit.
- DFLT_CYCLES
- Cycles CPU is using Deflate unit.
- DFLT_CC
- Increments by one for every DEFLATE CONVERSION CALL instruction executed that ended in Condition
Codes 0, 1, or 2.
Issue the lscpumf command with the -C option to find out how
these names map to the counter numbers on your IBM® Z hardware.
In the edition of IBM The CPU-Measurement
Facility Extended Counters Definition for z10, z196/z114, zEC12/zBC12, z13®/z13s®, z14, z15® and z16,
SA23-2261 for your hardware model, the
counters are listed by counter number.
For information about working with hardware counters, see Using the CPU-measurement facilities.
