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Subject: Re: [OMPI devel] v1.5 r25914 DOA
From: Ralph Castain (rhc_at_[hidden])
Date: 2012-02-22 14:08:31

On Feb 22, 2012, at 11:59 AM, Brice Goglin wrote:

> Le 22/02/2012 17:48, Ralph Castain a écrit :
>> On Feb 22, 2012, at 9:39 AM, Eugene Loh wrote:
>>> On 2/21/2012 10:31 PM, Eugene Loh wrote:
>>>> ... "sockets" is unknown and hwloc returns 0 for num_sockets and OMPI pukes on divide by zero. OS info was listed in the original message (below). Might we want to do something else? E.g., assume num_sockets==1 when num_sockets==0 (if you know what I mean)? So, which one (or more) of the following should be fixed?
>>>> *) on this platform, hwloc finds no socket level
>>>> *) therefore hwloc returns num_sockets==0 to OMPI
>>>> *) OMPI divides by 0 and barfs on basically everything
>>> Okay. So, Brice's other e-mail indicates that the first two are "not really uncommon":
>>> On 2/22/2012 7:55 AM, Brice Goglin wrote:
>>>> Anyway, we have seen other systems (mostly non-Linux) where lstopo
>>>> reports nothing interesting (only one machine object with multiple PU
>>>> children). So numsockets==0 isn't really uncommon.
>>> So, it seems to me that OMPI needs to handle the num_sockets==0 case rather than just dividing by num_sockets. This is v1.5 orte_odls_base_open() since r25914.
>> Unfortunately, just artificially setting the num_sockets to 1 won't solve much - you'll get past that point in the code, but attempts to bind are likely to fail down the road. Fixing it will require some significant effort.
>> Given we haven't heard reports of this before, I'm not convinced it is a widespread problem. For now, let's just use the mca param and see what happens.
> I am probably missing something but: Why would setting num_sockets to 1
> work fine as a mca param, while artificially setting it as said above
> wouldn't ?

Because the param means that it isn't hardwired into the code base. I want to first verify that artificially forcing num_sockets to 1 doesn't break the code down the road, so the less change to find out, the better.

> Brice
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