On Thu, 24 Apr 2014, Philip Mucci wrote:
> But Vince, are you implying that we should kinda ‘discourage’ using
> these events? I think we want people (experts like Gary) to be able to
> measure an uncore event with all information. As is stands,
> understanding events at that level falls on the user. Stephane shot down
> the idea of libpfm changing - unfortunately, that leaves us to find a
> workaround in PAPI. I don’t think we can throw out a valuable solution
> just because it covers 99% (rather than 100) of the installed user base.
> I want to understand your proposal for the solution, what are your
> thoughts?
I'm just saying maintanence wise it's going to be a pain if we have two
different ways of doing the same thing. Just looking at the bigger
picture.
Ideally we should be able to use the CPU= flag on any event, not just
uncore. But to do that properly PAPI should be handling the flag, not
libpfm4.
Otherwise you end up with the problem where Linux/libpfm4 users can just
do something like
UNHALTED_CORE_CYCLES:cpu=0
but the interface is completely different if you're saying running on
BlueGene, etc, and you have to go through the whole setopt interface.
It means the whole cross-platform idea of PAPI falls apart because you
might as well be using two different libraries, PAPI, and PAPI-libpfm4
which have different ways of doing things and will require different
#ifdefs in your code depending on what OS you're running your code on.
So yes, we can throw together some sort of short-term hack that gets
uncore working a little easier right now (it's perfectly possible to get
uncore results even without the cpu=0 patches, you just need to use CPU
attach like the example code shoes). It's just going to add a long-term
maintanence pain to the rest of the library.
Vince------------------------------------------------------------------------------
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