Every counter belongs to a counter class. The class determines which filters are available for the counter.
the following basic classes of counters:
- Absolute counters, for example Memory:
Free, report the current, absolute value. Use the
minimum filters with
- Delta counters, for example Clock:
Cycles, report the number of occurrences since the last
measurement. The exact time when the data occurs is unknown, so data is
interpolated between timestamps. Use the
with delta counters.
- Incident counters, for example Kmem: kmalloc, are the same as delta counters, except the exact
time is known when the data occurs, so no interpolation is calculated.
- Activity counters, for example Contention:
Wait, report changes in processor activity or state. Use the
average filter with activity
For counters other than Activity counters, the data is calculated for
1ms resolution even in a high-resolution report. The high resolution zoom levels for
these counters show interpolated values based on the 1ms data.
The following figure illustrates how the same data received from gator appears
differently, depending on the counter class. In each case, the value 10 occurs at the
4.999ms timestamp, and the value 6 occurs at 6.999ms. The red lines shows the counter
value at 1ms time intervals.
NoteIn the delta counter chart, the value of 10 at 4.999ms is amortized from
5ms back to 0ms, because there is no other value, so its value is 2 for that period. The
value of 6 at 6.999ms is amortized from 7ms back to 5ms, which is when the last value
was received, so its value is 3 for that period.
Figure 5-40 Counter classes