Cristian Perfumo wrote:
Some days ago I sent an email to the list asking about the reason why I
couldn't run my programs with the "-Nx" RTS option even if I compiled
them with -threaded.
AH! by the way, the architecture is ia64 (Itanium).
Today I realized that when I ./configure, a preprocessor variable called
"NOSMP" is defined and it disallows the multiple OS threads (the -Nx
option).
Looking a bit deeper I figured out that there's no Itanium version for
the functions xchg (exchange), cas (compare-and-swap) and write_barrier
in the header file SMP.h (includes/SMP.h) so there's no way that the
holy -N option is available.
My question is: is it enough to implement xchg, cas and write_barrier
for ia64 to make multiple OSthreads available on ia64? If not, what else
should be implemented/changed?
Yes, that should be enough. The main concern is that on architectures that
don't have strong memory ordering, that the thunk update sequence is safe. See
section 3.3:
http://www.haskell.org/~simonmar/papers/multiproc.pdf
At the moment the update code contains a memory barrier, which compiles to
nothing on x86/x86_64 (see SMP.h:write_barrier()). You should check that this
doesn't impose a significant performance penalty on ia64: try one of the
benchmarks that does a lot of updates (e.g. nofib/imaginary/exp3_8) with and
without -threaded.
Cheers,
Simon
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