swift-dev-boun...@swift.org wrote on 02/16/2017 09:48:28 PM: > > I was curious about the overhead of ARC and started profiling some > benchmarks found in the Computer Language Benchmark Game (http:// > benchmarksgame.alioth.debian.org/u64q/measurements.php?lang=swift). > So far, it seems that ARC sequence optimization is surprisingly good > and most benchmarks don't have to perform ARC operations as often as > I expected. I have some questions regarding this finding. > > I compiled all benchmarks with "-O -wmo" flags and counted the > number of calls to ARC runtime (e.g., swift_rt_swift_retain) using Pin. > > 1. Reference counting is considered to have high overhead due to > frequent counting operations which also have to be atomic. At least > for the benchmarks I tested, it is not the case and there is almost > no overhead. Is it expected behavior? Or is it because the > benchmarks are too simple (they are all single-file programs)? How > do you estimate the overhead of ARC would be? > hmm, I wonder if your method of profiling is really finding all the ARC operations. The Swift version of regex-dna is about 25x slower than the Java version (on Linux). I looked at some prof profiles about a month ago and at the time roughly 80% of all execution samples were attributed to swift_retain/swift_release operations coming from CoreFoundation's regex implementation. --dave (See attached file: regex-dna.svg)
regex-dna.svg
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