HP Caliper User's Guide

threadswitch Event Set
Available only on dual-core Itanium 2 systems.
The threadswitch event set provides data about the impact of HyperThreading on
the measured process. It provides a full statistical breakdown of thread switch activity.
HyperThreading (formally called Hyper-Threading Technology) provides the ability
for a processor to create an additional logical processor that might allow additional
efficiencies of processing. For example, a dual-core Itanium 2 processor with
HyperThreading active provides four logical processors, two on each core. An Itanium
9300 quad-core processor with HyperThreading active provides eight logical processors.
This allows the operating system to schedule two threads or processes simultaneously.
The effect that HyperThreading has on performance depends heavily on the application.
HyperThreading can increase the overall throughput of an application, but individual
processes are usually slowed down by it.
If you use this event set, the default is to make the measurements irrespective of CPU
operating state (that is, user, system, or interrupt states). By default, the idle state is
not included in the measurement. You can use command-line options to limit the scope
of the measurement. Specifically, you can:
• Limit measurement to a specific privilege level: -m
event_set[:all|user|kernel]
• Include idle: --exclude-idle False
• Exclude the interruption state: --measure-on-interrupts off
• Only measure the interruption state: --measure-on-interrupts only
Metrics Available from this Measurement
The following metrics are available from this event set. These descriptions do not take
into account any command-line options you might use.
The metrics are:
• TS Per Sec
Number of thread switches each second.
• TS Per Kinst
Number of thread switches every 1000 instructions.
• L3miss
Percentage of all thread switches that were caused by a miss in the Level 3 cache.
A large value indicates a “good” use of HyperThreading: while this process is
waiting on memory, another process can execute.
• Timer
Percentage of all thread switches due to the “fair share” timer. A large value
indicates a “poor” use of HyperThreading: both processes are competing for
processor execution cycles.
344 Event Set Descriptions for CPU Metrics