#2466: Execution time mis-accounting
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Reporter: heatsink | Owner:
Type: bug | Status: new
Priority: normal | Component: Profiling
Version: 6.8.2 | Severity: normal
Keywords: | Testcase:
Architecture: x86 | Os: Linux
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In the attached test case, profiling assigns a large fraction of run time
to a single function. The fraction ranges from 19% to 40% across runs.
Although I haven't independently verified the profile, I believe execution
time is mis-attributed to this function.
The function in question is:
{{{
intersect :: Object -> Ray -> Maybe Intersection
intersect obj@(Object dat mem) = objmIntersect mem dat obj
}}}
where `objmIntersect` is a field selector. In `-ddump-simpl` output, the
function consists of two case statements and a function call. The
function it calls has its own SCC.
In profiling, this function is usually listed as the most time-consuming
function in the program. Its callee is assigned a similar amount of time.
Both functions are called the same number of times. The callee computes a
ray-triangle intersection, which is presumably more time-consuming than
two case statements and a function call...
{{{
COST CENTRE MODULE %time %alloc
intersect Datatypes 28.5 11.3
triangle.intersect Triangle 25.0 2.0
(other functions...)
}}}
I've reduced the test case from a somewhat larger ray tracer. I'm willing
to help reduce it further if needed. The test case depends on the
[http://haskell.org/haskellwiki/Vector-space vector-space] library.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2466>
GHC <http://www.haskell.org/ghc/>
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