Threaded RTS performing badly on recent OS X (10.8?)
|Reported by:||simonmar||Owned by:||thoughtpolice|
|Keywords:||thread-local state, TLS clang||Cc:||johan.tibell@…, chak@…, anton.nik@…, george.colpitts@…, simonmar|
|Operating System:||MacOS X||Architecture:||x86_64 (amd64)|
|Type of failure:||Runtime performance bug||Test Case:|
|Related Tickets:||Differential Rev(s):|
This ticket is to remind us about the following problem: OS X is now using llvm-gcc, and as a result GHC's garbage collector with -threaded is much slower than it should be (approx 30% slower overall runtime). Some results here: http://www.haskell.org/pipermail/cvs-ghc/2011-July/063552.html
This is because the GC code relies on having fast access to thread-local state. It uses one of two methods: either a register variable (gcc only) or
__thread variables (which aren't supported on OS X). To make things work on OS X, we use calls to
pthread_getspecific instead (see #5634), which is quite slow, even though it compiles to inline assembly.
I don't recall which OS X / XCode versions are affected, maybe a Mac expert could fill in the details.
We have tried other fixes, such as passing around the thread-local state as extra arguments, but performance wasn't good. Ideally Apple will implement TLS in OS X at some point and we can start to use it.
A workaround is to install a real gcc (using homebrew?) and use that to compile GHC. Whoever builds the GHC distributions for OS X should probably do it that way, so everyone benefits.
Change History (56)
comment:14 Changed 4 years ago by
|Architecture:||Unknown/Multiple → x86_64 (amd64)|
|Operating System:||Unknown/Multiple → MacOS X|
|Owner:||set to thoughtpolice|
|Version:||7.6.1 → 7.7|
comment:39 Changed 3 years ago by
|Keywords:||thread-local state TLS clang added|
|Type of failure:||None/Unknown → Runtime performance bug|