[petsc-dev] odd log behavior

Wed Apr 27 10:06:40 CDT 2022

  Only KSPSolve, SNESSolve, TSSolve will have legitimate values. "High-level" functions like PtAP can be asynchronous (meaning the GPU returns to the CPU to do more stuff) before they are complete, hence their timings would be incorrect and so they must be labeled with a special marker and not have numbers for time.

  Jed reports a possible 10% smaller time for KSPSolve() in this mode in some of his runs, compared to timing correctly the inner operations, and thus feels it is the best default.

  Barry

> On Apr 27, 2022, at 10:08 AM, Mark Adams <mfadams at lbl.gov> wrote:
> 
> 
> 
> On Tue, Apr 26, 2022 at 8:00 PM Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> wrote:
> 
>   The current nan output has to be replaced to get the column alignment correct, I just didn't feel like making that change also in the same MR. 
> 
>   Something like Unknown or anything that fits in the column space would be fine. It just means for the given run the timing numbers are not meaningful/correct for those events.
> 
> Just a note, just about every event is NAN for me. My GAMG setup that is all CPU is NAN. High level functions like PtAP as well. 
> That said, adding -log_view_gpu_time is fine. Not worth the churn.
>  
> This is to obtain the best meaningful results for the outer events per Jed since timing the inner events accurately introduces extra time in the outer events. That is it is not possible to have the best accurate times for both inner events and outer events in the same run. So if you want to compare KSPSolve timings, for example, you run as-is, it you want to examine, low-level vector operations run also with -log_view_gpu_time but know that the KSP times are higher than need be.
> 
>   Sorry for the confusion.
> 
> 
> 
> 
>> On Apr 26, 2022, at 3:49 PM, Matthew Knepley <knepley at gmail.com <mailto:knepley at gmail.com>> wrote:
>> 
>> On Tue, Apr 26, 2022 at 12:03 PM Mark Adams <mfadams at lbl.gov <mailto:mfadams at lbl.gov>> wrote:
>> Well, Nans are a clear sign that something is very wrong.
>> 
>> Barry chose them so that it could not be mistaken for an actual number.
>> 
>>    Matt
>>  
>> On Tue, Apr 26, 2022 at 11:52 AM Jacob Faibussowitsch <jacob.fai at gmail.com <mailto:jacob.fai at gmail.com>> wrote:
>> There is an automatic warning that shows when you do run with `-log_view_gpu_time`, but perhaps there should also be an automatic warning when *not* running with it. It is unfortunate that NaN is the value printed as this implies a bug but AFAIK it is unavoidable (Barry can say more on this though).
>> 
>> Best regards,
>> 
>> Jacob Faibussowitsch
>> (Jacob Fai - booss - oh - vitch)
>> 
>> > On Apr 26, 2022, at 09:48, Jose E. Roman <jroman at dsic.upv.es <mailto:jroman at dsic.upv.es>> wrote:
>> > 
>> > You have to add -log_view_gpu_time
>> > See https://gitlab.com/petsc/petsc/-/merge_requests/5056 <https://gitlab.com/petsc/petsc/-/merge_requests/5056>
>> > 
>> > Jose
>> > 
>> > 
>> >> El 26 abr 2022, a las 16:39, Mark Adams <mfadams at lbl.gov <mailto:mfadams at lbl.gov>> escribió:
>> >> 
>> >> I'm seeing this on Perlmutter with Kokkos-CUDA. Nans in most log timing data except the two 'Solve' lines.
>> >> Just cg/jacobi on snes/ex56.
>> >> 
>> >> Any ideas?
>> >> 
>> >> VecTDot                2 1.0   nan nan 1.20e+01 1.0 0.0e+00 0.0e+00 0.0e+00  0  0  0  0  0   0  0  0  0  0  -nan    -nan      0 0.00e+00    0 0.00e+00 100
>> >> VecNorm                2 1.0   nan nan 1.00e+01 1.0 0.0e+00 0.0e+00 0.0e+00  0  0  0  0  0   0  0  0  0  0  -nan    -nan      0 0.00e+00    0 0.00e+00 100
>> >> VecCopy                2 1.0   nan nan 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00  0  0  0  0  0   0  0  0  0  0  -nan    -nan      0 0.00e+00    0 0.00e+00  0
>> >> VecSet                 5 1.0   nan nan 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00  0  0  0  0  0   0  0  0  0  0  -nan    -nan      0 0.00e+00    0 0.00e+00  0
>> >> VecAXPY                4 1.0   nan nan 2.40e+01 1.0 0.0e+00 0.0e+00 0.0e+00  0  0  0  0  0   1  0  0  0  0  -nan    -nan      0 0.00e+00    0 0.00e+00 100
>> >> VecPointwiseMult       1 1.0   nan nan 3.00e+00 1.0 0.0e+00 0.0e+00 0.0e+00  0  0  0  0  0   0  0  0  0  0  -nan    -nan      0 0.00e+00    0 0.00e+00 100
>> >> KSPSetUp               1 1.0   nan nan 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00  0  0  0  0  0   0  0  0  0  0  -nan    -nan      0 0.00e+00    0 0.00e+00  0
>> >> KSPSolve               1 1.0 4.0514e-04 1.0 5.50e+01 1.0 0.0e+00 0.0e+00 0.0e+00  1  0  0  0  0   2  0  0  0  0     0    -nan      0 0.00e+00    0 0.00e+00 100
>> >> SNESSolve              1 1.0 2.2128e-02 1.0 5.55e+05 1.0 0.0e+00 0.0e+00 0.0e+00 72 56  0  0  0 100100  0  0  0    25    -nan      0 0.00e+00    0 0.00e+00  0
>> > 
>> 
>> 
>> 
>> -- 
>> 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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