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Subject: Re: [hwloc-devel] Pgcc issues fixed?
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-11-09 08:05:47

On Nov 9, 2009, at 5:12 AM, Samuel Thibault wrote:

> What I dislike in that approach is that it means we'd have to closely
> follow future changes in the kernel ABI, while the API is not supposed
> to change (even if it has in the past). Also, now that glibc provides
> pthread_setaffinity_np, we should take advantage of it to implement
> hwloc_set_thread_cpubind, and there is no way we can re-implement it
> ourselves (the missing piece is the pthread_t -> tid translation).

Fair enough. What about if we have an AC check for
pthread_setaffinity_np and use that if it exists, and if it doesn't
use the PLPA way? So if the timeline looks like this:

----- way in the past (time flows down)
   -----> "bad" setaffinity days of kernel/glibc mixing
   | PLPA method is known to work here
   -----> pthread_setaffinity_np is introduced, fixes problems
----- present

Then if AC causes hwloc to prefer pthread_setaffinity_np(), then we're
covered for all the old systems with either old kernels and/or old
glibc where problems occur.

BTW, how does pthread_setaffinity_np() work? Does it check the
running kernel and ensure to do the Right Thing? That was definitely
a problem in the past -- kernel and glibc would mismatch in terms of
set/getaffinity (which was included in many distros).

Jeff Squyres