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From: George Bosilca (bosilca_at_[hidden])
Date: 2007-07-14 13:16:42


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.

   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
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