[Cado-nfs-discuss] OpenMP Usage

Robert Pancoast robertpancoast77 at gmail.com
Sun Nov 18 17:59:12 CET 2018

Hello Emmanuel,

I greatly appreciate your insight. Can you please provide more details as to why the GPUs do not work for sieving? I am curious about sieve subprogram and it’s details. 


> On Nov 15, 2018, at 8:21 AM, Emmanuel Thomé <Emmanuel.Thome at inria.fr> wrote:
> No.
> (long answer: absolutely no interest in exploring GPUs for sieving.
> Return over investment is not even provably positive).
> E.
>> On Thu, Nov 15, 2018 at 05:43:48AM -0500, Robert Pancoast wrote:
>> Hello Emmanuel,
>> Thanks for the information. I am specifically curious about OpenMP because the latest release supports offload to Nvidia GPU. What are your thoughts on accelerating the Cado-nfs system with GPU?
>> Thanks,
>> Robert
>>>> On Nov 15, 2018, at 2:35 AM, Emmanuel Thomé <Emmanuel.Thome at inria.fr> wrote:
>>>> On Wed, Nov 14, 2018 at 07:06:23PM -0500, Robert Pancoast wrote:
>>>> Hello Emmanuel,
>>>> I appreciate the insight.  Is it possible to convert the subprograms
>>>> that use C++11 threads.and posix threads to use OpenMP?
>>> Probably not, and we won't do that anyway. These are three different
>>> interfaces to mostly the same bare bones, and it's pointless to express a
>>> strong preference or dislike for one versus the others. All have pros and
>>> cons. The idea of convenience or habits for the person programming the
>>> software comes first.
>>>> Additionally,
>>>> which subprograms compose the majority of execution time throughout
>>>> factorization?
>>> sieving (aka "las" in cado-nfs).
>>> E.
>>>> Thanks,
>>>> Robert
>>>>>> On Wed, Nov 14, 2018 at 2:54 AM Emmanuel Thomé <Emmanuel.Thome at inria.fr> wrote:
>>>>>> On Tue, Nov 13, 2018 at 09:22:07PM -0500, Robert Pancoast wrote:
>>>>>> Greetings,
>>>>>> I have an interest in further exploring cado-nfs usage, but it has been quite some time since I have looked into the sources. In the current codebase, does there exist openMP usage? What are the major stages of a factorization, and which (if any) utilization openMP?
>>>>> Hi,
>>>>> cado-nfs does use openmp. More broadly, cado-nfs has been using threads
>>>>> from day one. This being said, cado-nfs comprises many subprograms, and
>>>>> their use of threads varies. Here's a quick recap off the top of my head
>>>>> (with some help from "git grep"):
>>>>> polyselect:
>>>>>   main program uses posix threads.
>>>>>   root optimization uses openmp.
>>>>>   DL polyselect uses openmp.
>>>>> sieve:
>>>>>   "makefb" uses posix threads.
>>>>>   "las" uses posix threads and C++11 threads.
>>>>>   "batch cofactorization" uses openmp.
>>>>> filter:
>>>>>   heavylifting of relation i/o uses posix threads (with minimalist
>>>>>   locking) (this is pervasive in almost all of the filter code).
>>>>>   some spots in "merge" and "replay" use openmp.
>>>>> linear algebra:
>>>>>   most of the code uses posix threads, as well as MPI.
>>>>>   linear generator computation uses openmp and MPI (subject to evolve soon).
>>>>> other:
>>>>>   "characters" and "sqrt" use posix threads.
>>>>>   "crtalgsqrt" uses posix threads and MPI.
>>>>> Whether some code is written to use posix threads or openmp or c++11
>>>>> threads or whatnot depends on multiple factors. Some things are best done
>>>>> in one model rather than another. Some of the authors have a preference
>>>>> towards one model rather than another, too.
>>>>> E.

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