Lecture Notes in Computer Science 4917

390 Y. Ben Asher et al.
35%
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Performance improvement on Power4
inline all exec funcs inline hot funcs
inline small funcs inline dominant calls
ILB
gcc pars tw olf perlb bzip2 crafty vortex eon gzip gap vpr m cf Avg
Performance improvement on 440GX
inline all exec funcs inline hot funcs
inline small funcs inline dominant calls
ILB
gcc pars tw olf perlb bzip2 crafty vortex eon gzip gap vpr m cf Avg
Fig. 3. Performance improvements on the Power4 (top) and 440GX (bottom)
inlining methods that are based on combinations of size and temperature. The
improvements on the embedded CPU are smaller than those on the server. This
can be explained by the fact that the Icache on the AMCC 440GX is highly associative.
Therefore, conflicting inlinings on the Power4’s direct-mapped Icache
do not conflict on the 440GX’s associative Icache.
Figure 4 depicts the number of function inlined by each method. Note that
ILB inlined less functions than most of the other methods yet obtained a higher
performance. This suggests that the ILB scheme inlines the “correct” set of
functions. Moreover, there is a clear correlation between inlining to many functions
and performance degradation, demonstrating the need for “precise” inlining
methods.
2.2 Removing Cold Edges
Here we describe in detail how “cold” edges are removed from the call graph,
and are not considered for inlining. The algorithm is based on a threshold that
indicates which edges are considered cold. The experimental results verify that
each program requires a different threshold in order to maximize the performance
of aggressive inlining. This requires a normalization procedure of the profile
information as follows: