[petsc-users] Various Questions Regarding PETSC

[Mohammed Mostafa]

Hello Barry,

> In runs did you zero the matrix before call the MatSetValues() initially?
>
I only zero the matrix when using add_values insert mode but otherwise I
don’t


> What kind of a processor is this?
This is an i7-Processor 6 core 3.9Ghz if I can remember correctly
I tried it on another intel Xeon processor 14 core but using only 6
processor and I got a similar trend with increasing nrow buffer

> Would you be able to run the code under gprof, vtune, instruments or
something profiling package that gives line by line information about time
being spent. In particular I'd like to see the results for MatSetValues(),
MatSetValues2() with 1 row, with 2, rows and with 4 rows.
>
I will try to do that but I am currently traveling to attend a conference
so I can not get back to you on that until Thursday


Regards,
Kamra


> On Jul 20, 2019, at 8:59 AM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:
>
> In runs did you zero the matrix before call the MatSetValues() initially?
>
>
>> MatSetValues()
>> FillPetscMat     3.6594e+00
>> MatSetValues2_MPIAIJ() with an nrow_buffer = 1
>> FillPetscMat     13.3920e+00
>> nrow_buffer = 2
>> FillPetscMat_with_MatSetValues2                  3.3321e+00
>> nrow_buffer = 5
>> FillPetscMat_with_MatSetValues2                  2.8842e+00
>> nrow_buffer = 10
>> FillPetscMat_with_MatSetValues2                  2.7669e+00
>> nrow_buffer = 20
>> FillPetscMat_with_MatSetValues2                  2.6834e+00
>> nrow_buffer = 50
>> FillPetscMat_with_MatSetValues2                  2.6862e+00
>> nrow_buffer = 100
>> FillPetscMat_with_MatSetValues2                  2.6170e+00
>>
>
> The call to MatSetValues() has a little bit of checking and then another
call to MatSetValues_MPIAIJ() so it is not surprising that going directly
> to MatSetValues_MPIAIJ2() saves you a bit but it is a large savings than
I would expect.
>
> I am greatly puzzled by the dramatic savings you get as you pass more
rows to MatSetValues2. As far as I can see all you are saving is a function
call, not much of anything else and that would NOT explain the huge time
savings (functions calls are extremely cheap compared to .5 seconds. The
multi row MatSetValues2() still has to do the same processing as with one
call per row so why so much faster?
>
> What kind of a processor is this?
>
> Would you be able to run the code under gprof, vtune, instruments or
something profiling package that gives line by line information about time
being spent. In particular I'd like to see the results for MatSetValues(),
MatSetValues2() with 1 row, with 2, rows and with 4 rows.
>
>
>
> Thanks
>
>   Barry
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