[Cado-nfs-discuss] OpenMP Usage

Robert Pancoast robertpancoast77 at gmail.com
Thu Nov 15 11:43:48 CET 2018

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?


> 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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