#5282: Bizarre results from -P profiler on OS X
-------------------------------+--------------------------------------------
Reporter: bos | Owner:
Type: bug | Status: new
Priority: normal | Component: Runtime System
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: MacOS X | Blocking:
Architecture: x86_64 (amd64) | Failure: Incorrect result at runtime
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I'm trying to use the profiler to understand the performance of an
application on OS X. I have a smallish benchmark that prints a lot of
lines of text to `stdout`, and the numbers reported when I use `+RTS -P`
are very different from what I see with my eyes.
The benchmark itself is quite simple:
https://github.com/mailrank/text-format/blob/master/benchmarks/Simple.hs
When I run it on the command line, it produces simple enough output:
{{{
$ time ./Simple one 500000 +RTS -P >/dev/null
500000 iterations in 2.6 secs (191.7 thousand/sec)
real 0m2.626s
user 0m2.586s
sys 0m0.030s
}}}
The time measured within the app and the wallclock time are both in
agreement.
However, if I look at the `Simple.prof` file left behind afterwards, its
numbers seem bizarre:
{{{
Mon Jun 27 11:35 2011 Time and Allocation Profiling Report
(Final)
Simple +RTS -P -RTS one 500000
total time = 0.28 secs (14 ticks @ 20 ms)
total alloc = 2,200,395,720 bytes (excludes profiling overheads)
}}}
It reports a time of just 0.28 seconds, and the number of ticks it counts
arithmetically agree with this.
I have other programs that suffer from the same discrepancy between
wallclock measurement and what the profiler reports to me, such that I
don't feel like I can trust the profiler at all here. I'm at a loss for
what to do about this, though.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5282>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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