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8.5. Assessment of Performance Characteristics
ment of the OMOP enabled. Only if that is the case, are additional checks and
a potential invocation of the corresponding intercession handler performed.
Thus, for the given benchmarks, the overhead consists of the additional check
and the consequence of the additional code, which may cause cache misses.
8.5.3. Customization Constant Assessment
Context and Rationale As discussed in Sec. 7.2.1, the RoarVM+OMOP uses
an optimization to avoid invoking a domain’s intercession handler when it
has not been customized. Originally, the optimization was added to ease
debugging and reduce noise introduced by executing standard intercession
handlers, which only implement standard language semantics. However, this
optimization is not without drawbacks because it introduces a number of
memory accesses and tests for all bytecodes that require modifications for
the OMOP. The code that runs unenforced most likely incurs only a minor
performance penalty. However, the effect on enforced execution is likely to
be more pronounced. Specifically, code that runs in the context of domains
that customize a majority of the intercession handlers is likely to experience
overhead caused by additional checks. On the other hand, this optimization
should yield performance benefits for code that runs in the context of domains
that customize only a limited subset of the intercession handlers.
In order to assess the performance impact, a variant of RoarVM+OMOP
(opt) is used that performs no additional tests but invokes the intercession
handlers unconditionally. This variant with full intercession activation is referred
to as RoarVM+OMOP (full).
Overhead during Unenforced Execution Fig. 8.8 24 depicts the results measured
for the kernel benchmarks for unenforced execution. Results vary from
small performance benefits of ca. 3% to slowdowns of up to 4%. The average
slowdown is 1%. Changes in performance are solely caused by the existence
of additional code in the bytecode’s implementation. Since the experiment
used unenforced execution, this additional code was not executed. In conclusion,
all measured effects are either caused by increased code size, triggering
certain compiler heuristics, or other similar effects. Since the results are mixed
and on average only show a difference of 1%, the overall effect on unenforced
execution is negligible.
24 The beanplot library of R forced a linear scale for this graph.
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