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8.5. Assessment of Performance Characteristics
ceptable in situations where the OMOP significantly simplifies the implementation
of concurrent programming concepts or a VM-based solution is not yet
available.
8.5. Assessment of Performance Characteristics
In order to understand the performance characteristics of the OMOP implementations,
different aspects of the changed execution model need to be evaluated.
Thus, the overhead of executing a program in the context of the OMOP
is evaluated by measuring the cost of reifying operations, i. e., executing them
reflectively. Furthermore, the experiments measure the inherent overhead that
is introduced by the chosen implementation approach for the OMOP. Finally,
the performance impact of the customization constant (cf. Sec. 8.5.3) for the
RoarVM+OMOP is measured to determine the cost and benefit of this optimization.
8.5.1. OMOP Enforcement Overhead
Context and Rationale In the worst case customizing language behavior by
using a MOP has the overhead of performing operations reflectively instead
of directly. The OMOP in combination with Smalltalk represents this worst
case, because the available metaprogramming facilities require that intercession
handlers use reflective operations, which have an inherent overhead.
The evaluation needs to determine in which order of magnitude the overhead
for these reflective operation lies to assess the practicality. Knowledge
of this overhead can guide the implementation of concurrent programming
concepts on top of the OMOP and helps explaining their performance.
Setup To measure the enforcement overhead, the kernel benchmarks are
executed unchanged with enforcement enabled. The code executes within
the standard Domain (cf. Fig. 5.1). Thus, the intercession handler only implements
standard semantics of the operation they represent. For example,
#requestExecOf:on:with:lkup: merely invokes the requested method reflectively,
and #readField:of: as well as #write:toField:of: perform the corresponding
read or write on the object field.
The overhead that is measured by this benchmark is the minimal overhead
for a fully customized domain. Domains that customize only subsets of the
intercession handler might have lower overhead, especially if the OMOP implementation
checks the customization constant (cf. Sec. 7.2.1).
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