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From: Gleb Natapov (glebn_at_[hidden])
Date: 2007-07-14 13:51:08


On Sat, Jul 14, 2007 at 01:16:42PM -0400, George Bosilca wrote:
> Instead of failing at configure time, we might want to disable the
> threading features and the shared memory device if we detect that we
> don't have support for atomics on a specified platform. In a non
> threaded build, the shared memory device is the only place where we
> need support for memory barrier. I'll look in the code to see why we
> need support for compare-and-swap on a non threaded build.
Proper memory barrier is also needed for openib BTL eager RDMA support.

>
> Thanks,
> george.
>
> On Jul 14, 2007, at 1:06 PM, Brian Barrett wrote:
>
> > On Jul 14, 2007, at 10:53 AM, Dirk Eddelbuettel wrote:
> >
> >> Methinks we need to fill in a few blanks here, or make do with non-
> >> asm
> >> solutions. I don't know the problem space that well (being a
> >> maintainer
> >> rather than upstream developer) and am looking for guidance.
> >
> > Either way is an option. There are really only a couple of functions
> > that have to be implemented:
> >
> > * atomic word-size compare and swap
> > * memory barrier
> >
> > We'll emulte atomic adds and spin-locks with compare and swap if not
> > directly implemented. The memory barrier functions have to exist,
> > even if they don't do anything. We require compare-and-swap for a
> > couple of pieces of code, which is why we lost our Sparc v8 support a
> > couple of releases ago.
> >
> >> For what it's worth, lam (7.1.2, currently) us available on all build
> >> architectures for Debian, but it may not push the (hardware)
> >> envelope as
> >> hard.
> >
> > Correct, LAM only had very limited ASM requirements (basically,
> > memory barrier on platforms that required it -- like PowerPC).
> >
> > Brian
> > _______________________________________________
> > devel mailing list
> > devel_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/devel
>
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--
			Gleb.