Configuring Counters
ARM DUI 0482K
Copyright © 2010-2012 ARM. All rights reserved.
5-6
ID120712
Non-Confidential
5.2.4
Energy Probe events
Energy probe events like power, current, and voltage do not appear in the list of available events
in the configuration counters dialog box. To configure what each channel measures and displays
in the Analysis Reports, you must modify the configuration.xml file. For more information, see
5.2.5
Events-based sampling
By default, Streamline records a sample at a an interval determined by the
Sample Rate
drop-down menu in the Capture Options dialog box. To override this, select an event from the
Events to Collect list and click the Toggle events-based sampling button on the right side of the
dialog box. This activates the
Threshold
field at the bottom of the Events to Collect list.
Note
Events-based sampling is only possible when the PMU on the target hardware can generate
interrupts.
Figure 5-5 Setting events-based sampling
When you have enabled events-based sampling, Streamline samples only when the selected
event is triggered a number of times equal to the value in the
Threshold
field, and does so for
each core on your target. For example, to trigger a sample every time a core causes 500 L2 cache
misses, select L2 miss from the Events to Collect list and enter
500
in the
Threshold
field. Given
an adequate capture session, the Samples statistic in many of the Streamline reports now
indicate which processes and functions are the potential cause of inefficient caching.
Note
Avoid setting a very low threshold for high frequency events. If you enter a Threshold value that
generates too many samples, Streamline could fail, and you might have to restart your target. To
find an appropriate value to enter in the
Threshold
field, turn off events-based sampling to run
a standard, time-based profile with the event counter that you want to use enabled. Look at the
resulting Analysis Report and note the peak per-second value in the chart for your counter. Your
target for the
Threshold
field is 1000 samples per second, so if the peak for that event is
2000000, a good value to insert in the
Threshold
field is 2000.
