#Rhealstone Benchmark
Dear DDJ,
I was very interested in your Rhealstone Real-Time Benchmark code in the
April issue. As a result I have developed the Rhealstone code for testing
DESQview using the DESQview C API. Now I am not suggesting that DESQview is
a real-time system but since it implements many of the capabilities of a
real-time systems I was interested in seeing the results.
When I reached the interrupt latency test I was stopped cold. I cannot see
where it measures anything but the CPU cycles to save the stack and perform
the 8254 latch operation. The way the test is constructed there is no
measurement of the operating system induced latency.
Throughout an operating system there are various tables which are updated
continuously. During updates to these tables interrupts are disabled to
prevent erroneous data entry. These disabled periods introduce delays in
responding to interrupts. It is these delays that cause interrupt latency.
The largest latency is typically during the processing of the real-time
clock tick when pre-emptive scheduling is required.
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