HMT and SMT Compared and Contrasted
Some key similarities and differences are:
y
SMT can improve throughput up to 40 per cent,
in rare cases, higher.
y
HMT typically improves throughput by 10 to 25
per cent.
y
SMT can allow QPRCMLTTSK to change at any
time.
y
HMT needs a full IPL for the change to
QPRCMLTTSK to be activated.
y
SMT has three values for QPRCMLTTSK ("0"
for off, also called "ST mode", "1" for on, and "2"
for "controlled" where OS/400 decides,
dynamically, whether to be in ST or SMT mode.
y
HMT operation is controlled by the system value
QPRCMLTTSK ("1" means active, "0" means
inactive)
y
SMT machines continue to report data on a
physical processor basis, but some of the
measurements are harder to interpret (reporting on
a logical CPU basis would be no better).
y
System performance counters and CPU
utilization values continue to be reported on a
physical CPU basis.
y
SMT complicates the question of measuring
CPU utilization.
y
CPU utilization measurements are not greatly
affected by HMT.
y
SMT allows multiple streams of execution
simultaneously.
y
HMT executes only one instruction stream at a
time.
y
SMT, because it is more dynamic, the SMT state
need not be identical across partitions.
y
All partitions have the same value for HMT
y
SMT can be turned on and off dynamically at
any time. No IPL required
y
HMT is can be turned on and off only by a
whole system IPL.
SMT Feature
HMT Feature
Models With/Without HMT
Not all prior models have HMT. In fact, some recent models have neither HMT nor SMT.
The following models have HMT available:
y
270, 800, 810, 820, 830, 840
The following have neither SMT nor HMT:
y
825, 870, 890
Earlier models than the 270 or 820 series (e.g. 170, 7xx, etc.) did not have either HMT nor SMT.
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
©
Copyright IBM Corp. 2008
Chapter 20 - General Tips and Techniques
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