Just chatted with Ralph about this on the phone and he came up with a slightly
better compromise...
He points out that we really don't need *all* of the hwloc API (there's a
bajillion tiny little accessor functions). We could provide a steady,
OPAL/ORTE/OMPI-specific API (probably down in opal/util or somesuch) with a
dozen or two (or whatever) functions that we really need. These functions can
either call their back-end hwloc counterparts or they could do something safe
if hwloc is not present / not supported / etc.
That would alleviate the need to put #if OPAL_HAVE_HWLOC elsewhere in the code
base. But the code calling opal_hwloc_<foo>() needs to be able to gracefully
handle the failure case where it returns OPAL_ERR_NOT_SUPPORTED (etc.).
On May 17, 2010, at 8:25 PM, Jeff Squyres (jsquyres) wrote:
> On May 17, 2010, at 7:59 PM, Barrett, Brian W wrote:
>
> > HWLOC could be extended to support Red Storm, probably, but we don't have
> > the need or time to do such an implementation.
>
> Fair enough.
>
> > Given that, I'm not really picky about what the method of not breaking an
> > existing supported platform is, but I think having HAVE_HWLOC defines
> > everywhere is a bad idea...
>
> We need a mechanism to have hwloc *not* be there, particularly for embedded
> environments -- where hwloc would add no value. This is apparently just like
> Red Storm, but even worse because we need to keep the memory footprint down
> as much as possible (libhwloc.so.0.0 on linux is 104KB -- libhwloc.a is 139KB
> -- both are big numbers when you only have a few MB of usable RAM). So even
> leaving stubs doesn't seem like a good idea -- they'll take up space, too.
> And the hwloc API is fairly large -- maintaining stubs for all the API
> functions could be a daunting task.
>
> I think embedding is the main reason I can't think of any better idea than
> #if OPAL_HAVE_HWLOC.
>
> I anticipate that hwloc usage would be fairly localized in the OMPI code base:
>
> int btl_sm_setup_stuff(...)
> {
> #if OPAL_HAVE_HWLOC
> ...do interesting hwloc things...
> ...setup stuff on btl_sm_component...
> btl_sm_component.have_hwloc = 1;
> #else
> btl_sm_component.have_hwloc = 0;
> #endif
> }
>
> int btl_sm_other_stuff(...)
> {
> if (btl_sm_component.have_hwloc) {
> ...use the hwloc info...
> }
> }
>
> But I'm certainly open to other ideas -- got any?
>
> --
> Jeff Squyres
> [email protected]
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
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--
Jeff Squyres
[email protected]
For corporate legal information go to:
http://www.cisco.com/web/about/doing_business/legal/cri/
