[petsc-users] chowiluviennacl

Xiangdong epscodes at gmail.com
Wed Jan 15 13:39:05 CST 2020 

I just submitted the issue: https://gitlab.com/petsc/petsc/issues/535

What I really want is an exact Block Tri-diagonal solver on GPU. Since for
block tridiagonal system, ILU0 would be the same as ILU. So I tried the
chowiluviennacl. but I found that the default parameters does not produce
the same ILU0 factorization as the CPU ones (PCILU). My guess is that if I
increase the number of sweeps chow_patel_ilu_config.sweeps(3), it may give
a better result. So the option Keys would be helpful.

Since Mark mentioned the Superlu's GPU feature, can I use superlu or
hypre's GPU functionality through PETSc?

Thank you.

Xiangdong

On Wed, Jan 15, 2020 at 2:22 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Jan 15, 2020 at 1:48 PM Xiangdong <epscodes at gmail.com> wrote:
>
>> In the ViennaCL manual
>> http://viennacl.sourceforge.net/doc/manual-algorithms.html
>>
>> It did expose two parameters:
>>
>> // configuration of preconditioner:
>> viennacl::linalg::chow_patel_tag chow_patel_ilu_config;
>> chow_patel_ilu_config.sweeps(3); // three nonlinear sweeps
>> chow_patel_ilu_config.jacobi_iters(2); // two Jacobi iterations per
>> triangular 'solve' Rx=r
>>
>> and mentioned that:
>> The number of nonlinear sweeps and Jacobi iterations need to be set
>> problem-specific for best performance.
>>
>> In the PETSc' implementation:
>>
>> viennacl::linalg::chow_patel_tag ilu_tag;
>>     ViennaCLAIJMatrix *mat = (ViennaCLAIJMatrix*)gpustruct->mat;
>>     ilu->CHOWILUVIENNACL = new
>> viennacl::linalg::chow_patel_ilu_precond<viennacl::compressed_matrix<PetscScalar>
>> >(*mat, ilu_tag);
>>
>> The default is used. Is it possible to expose these two parameters so
>> that user can change it through option keys?
>>
>
> Yes. Do you mind making an issue for it? That way we can better keep track.
>
> https://gitlab.com/petsc/petsc/issues
>
>   Thanks,
>
>     Matt
>
>
>> Thank you.
>>
>> Xiangdong
>>
>> On Wed, Jan 15, 2020 at 12:40 PM Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Wed, Jan 15, 2020 at 9:59 AM Xiangdong <epscodes at gmail.com> wrote:
>>>
>>>> Maybe I am not clear. I want to solve the block tridiagonal system
>>>> Tx=b a few times with same T but different b. On CPU, I can have it by
>>>> applying the ILU0 and reuse the factorization. Since it is block
>>>> tridiagonal, ILU0 would give same results as LU.
>>>>
>>>> I am trying to do the same thing on GPU with chowiluviennacl, but found
>>>> default factorization does not produce the exact factorization for
>>>> tridiagonal system. Can we tight the drop off tolerance so that it can work
>>>> as LU for tridiagonal system?
>>>>
>>>
>>> There are no options in our implementation. You could look at the
>>> ViennaCL manual to see if we missed something.
>>>
>>>   Thanks,
>>>
>>>     Matt
>>>
>>>
>>>> Thank you.
>>>>
>>>> Xiangdong
>>>>
>>>> On Wed, Jan 15, 2020 at 9:41 AM Matthew Knepley <knepley at gmail.com>
>>>> wrote:
>>>>
>>>>> On Wed, Jan 15, 2020 at 9:36 AM Xiangdong <epscodes at gmail.com> wrote:
>>>>>
>>>>>> Can chowiluviennacl do ilu0?
>>>>>>
>>>>>> I need to solve a tri-diagonal system directly. If I apply the PCILU,
>>>>>> I will obtain the exact solution with preonly + pcilu. However, the
>>>>>> preonly + chowiluviennacl will not provide the exact solution. Any option
>>>>>> keys to set the CHOWILUVIENNACL filling level or dropping off tolerance
>>>>>> like the standard ilu?
>>>>>>
>>>>>
>>>>> No. However, such a scheme makes less sense here. This algorithm
>>>>> spawns a individual threads for individual elements. Drop tolerance
>>>>> is not less work, it is sparser, but that should not matter for a
>>>>> tridiagonal system. Levels also is not applicable since you have only 1
>>>>> level.
>>>>>
>>>>>   Thanks,
>>>>>
>>>>>     Matt
>>>>>
>>>>>
>>>>>> Thank you.
>>>>>>
>>>>>> Best,
>>>>>> Xiangdong
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Tue, Jan 14, 2020 at 10:05 PM Matthew Knepley <knepley at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> On Tue, Jan 14, 2020 at 9:56 PM Xiangdong <epscodes at gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Dear Developers,
>>>>>>>>
>>>>>>>> I have a quick question about the chowiluviennacl. When I tried to
>>>>>>>> use it, I found that it only works for np=1, not np>1. However, in the
>>>>>>>> description of chowiluviennacl.cxx, it says "the ViennaCL Chow-Patel
>>>>>>>> parallel ILU preconditioner".
>>>>>>>>
>>>>>>>
>>>>>>> By parallel, this means shared memory parallelism on the GPU.
>>>>>>>
>>>>>>>
>>>>>>>> I am wondering whether I am using it correctly.
>>>>>>>> Does chowiluviennacl work for np>1?
>>>>>>>>
>>>>>>>
>>>>>>> I do not believe so. I do not see why it could not be extended, but
>>>>>>> that would mean writing some more code.
>>>>>>>
>>>>>>>   Thanks,
>>>>>>>
>>>>>>>     Matt
>>>>>>>
>>>>>>>
>>>>>>>> In addition, are there option keys for the chowiluviennacl one can
>>>>>>>> try?
>>>>>>>> Thank you.
>>>>>>>>
>>>>>>>> Best,
>>>>>>>> Xiangdong
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> What most experimenters take for granted before they begin their
>>>>>>> experiments is infinitely more interesting than any results to which their
>>>>>>> experiments lead.
>>>>>>> -- Norbert Wiener
>>>>>>>
>>>>>>> https://www.cse.buffalo.edu/~knepley/
>>>>>>> <http://www.cse.buffalo.edu/~knepley/>
>>>>>>>
>>>>>>
>>>>>
>>>>> --
>>>>> What most experimenters take for granted before they begin their
>>>>> experiments is infinitely more interesting than any results to which their
>>>>> experiments lead.
>>>>> -- Norbert Wiener
>>>>>
>>>>> https://www.cse.buffalo.edu/~knepley/
>>>>> <http://www.cse.buffalo.edu/~knepley/>
>>>>>
>>>>
>>>
>>> --
>>> What most experimenters take for granted before they begin their
>>> experiments is infinitely more interesting than any results to which their
>>> experiments lead.
>>> -- Norbert Wiener
>>>
>>> https://www.cse.buffalo.edu/~knepley/
>>> <http://www.cse.buffalo.edu/~knepley/>
>>>
>>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
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