[petsc-dev] MatMult on Summit
Karl Rupp
rupp at iue.tuwien.ac.at
Mon Sep 23 22:09:19 CDT 2019
Hi,
`git grep cudaStreamCreate` reports that vectors, matrices and scatters
create their own streams. This will almost inevitably create races
(there is no synchronization mechanism implemented), unless one calls
WaitForGPU() after each operation. Some of the non-deterministic tests
can likely be explained by this.
I'll clean this up in the next few hours if there are no objections.
Best regards,
Karli
On 9/24/19 1:05 AM, Mills, Richard Tran via petsc-dev wrote:
> I'm no CUDA expert (not yet, anyway), but, from what I've read, the
> default stream (stream 0) is (mostly) synchronous to host and device, so
> WaitForGPU() is not needed in that case. I don't know if there is any
> performance penalty in explicitly calling it in that case, anyway.
>
> In any case, it looks like there are still some cases where potentially
> asynchronous CUDA library calls are being "timed" without a WaitForGPU()
> to ensure that the calls actually complete. I will make a pass through
> the aijcusparse and aijviennacl code looking for these.
>
> --Richard
>
> On 9/23/19 3:28 PM, Zhang, Junchao wrote:
>> It looks cusparsestruct->stream is always created (not NULL). I don't
>> know logic of the "if (!cusparsestruct->stream)".
>> --Junchao Zhang
>>
>>
>> On Mon, Sep 23, 2019 at 5:04 PM Mills, Richard Tran via petsc-dev
>> <petsc-dev at mcs.anl.gov <mailto:petsc-dev at mcs.anl.gov>> wrote:
>>
>> In MatMultAdd_SeqAIJCUSPARSE, before Junchao's changes, towards
>> the end of the function it had
>>
>> if (!yy) { /* MatMult */
>> if (!cusparsestruct->stream) {
>> ierr = WaitForGPU();CHKERRCUDA(ierr);
>> }
>> }
>>
>> I assume we don't need the logic to do this only in the MatMult()
>> with no add case and should just do this all the time, for the
>> purposes of timing if no other reason. Is there some reason to NOT
>> do this because of worries the about effects that these
>> WaitForGPU() invocations might have on performance?
>>
>> I notice other problems in aijcusparse.cu <http://aijcusparse.cu>,
>> now that I look closer. In MatMultTransposeAdd_SeqAIJCUSPARSE(), I
>> see that we have GPU timing calls around the cusparse_csr_spmv()
>> (but no WaitForGPU() inside the timed region). I believe this is
>> another area in which we get a meaningless timing. It looks like
>> we need a WaitForGPU() there, and then maybe inside the timed
>> region handling the scatter. (I don't know if this stuff happens
>> asynchronously or not.) But do we potentially want two
>> WaitForGPU() calls in one function, just to help with getting
>> timings? I don't have a good idea of how much overhead this adds.
>>
>> --Richard
>>
>> On 9/21/19 12:03 PM, Zhang, Junchao via petsc-dev wrote:
>>> I made the following changes:
>>> 1) In MatMultAdd_SeqAIJCUSPARSE, use this code sequence at the end
>>> ierr = WaitForGPU();CHKERRCUDA(ierr);
>>> ierr = PetscLogGpuTimeEnd();CHKERRQ(ierr);
>>> ierr = PetscLogGpuFlops(2.0*a->nz);CHKERRQ(ierr);
>>> PetscFunctionReturn(0);
>>> 2) In MatMult_MPIAIJCUSPARSE, use the following code sequence.
>>> The old code swapped the first two lines. Since with
>>> -log_view, MatMultAdd_SeqAIJCUSPARSE is blocking, I changed the
>>> order to have better overlap.
>>> ierr =
>>> VecScatterBegin(a->Mvctx,xx,a->lvec,INSERT_VALUES,SCATTER_FORWARD);CHKERRQ(ierr);
>>> ierr = (*a->A->ops->mult)(a->A,xx,yy);CHKERRQ(ierr);
>>> ierr =
>>> VecScatterEnd(a->Mvctx,xx,a->lvec,INSERT_VALUES,SCATTER_FORWARD);CHKERRQ(ierr);
>>> ierr = (*a->B->ops->multadd)(a->B,a->lvec,yy,yy);CHKERRQ(ierr);
>>> 3) Log time directly in the test code so we can also know
>>> execution time without -log_view (hence cuda synchronization). I
>>> manually calculated the Total Mflop/s for these cases for easy
>>> comparison.
>>>
>>> <<Note the CPU versions are copied from yesterday's results>>
>>>
>>> ------------------------------------------------------------------------------------------------------------------------
>>> Event Count Time (sec) Flop
>>> --- Global --- --- Stage ---- Total GPU -
>>> CpuToGpu - - GpuToCpu - GPU
>>> Max Ratio Max Ratio Max Ratio Mess
>>> AvgLen Reduct %T %F %M %L %R %T %F %M %L %R Mflop/s Mflop/s
>>> Count Size Count Size %F
>>> ---------------------------------------------------------------------------------------------------------------------------------------------------------------
>>> 6 MPI ranks,
>>> MatMult 100 1.0 1.1895e+01 1.0 9.63e+09 1.1 2.8e+03
>>> 2.2e+05 0.0e+00 24 99 97 18 0 100100100100 0 4743 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterBegin 100 1.0 4.9145e-02 3.0 0.00e+00 0.0 2.8e+03
>>> 2.2e+05 0.0e+00 0 0 97 18 0 0 0100100 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterEnd 100 1.0 2.9441e+00 133 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 3 0 0 0 0 13 0 0 0 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>>
>>> 24 MPI ranks
>>> MatMult 100 1.0 3.1431e+00 1.0 2.63e+09 1.2 1.9e+04
>>> 5.9e+04 0.0e+00 8 99 97 25 0 100100100100 0 17948 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterBegin 100 1.0 2.0583e-02 2.3 0.00e+00 0.0 1.9e+04
>>> 5.9e+04 0.0e+00 0 0 97 25 0 0 0100100 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterEnd 100 1.0 1.0639e+0050.0 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 2 0 0 0 0 19 0 0 0 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>>
>>> 42 MPI ranks
>>> MatMult 100 1.0 2.0519e+00 1.0 1.52e+09 1.3 3.5e+04
>>> 4.1e+04 0.0e+00 23 99 97 30 0 100100100100 0 27493 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterBegin 100 1.0 2.0971e-02 3.4 0.00e+00 0.0 3.5e+04
>>> 4.1e+04 0.0e+00 0 0 97 30 0 1 0100100 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterEnd 100 1.0 8.5184e-0162.0 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 6 0 0 0 0 24 0 0 0 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>>
>>> 6 MPI ranks + 6 GPUs + regular SF + log_view
>>> MatMult 100 1.0 1.6863e-01 1.0 9.66e+09 1.1 2.8e+03
>>> 2.2e+05 0.0e+00 0 99 97 18 0 100100100100 0 335743 629278
>>> 100 1.02e+02 100 2.69e+02 100
>>> VecScatterBegin 100 1.0 5.0157e-02 1.6 0.00e+00 0.0 2.8e+03
>>> 2.2e+05 0.0e+00 0 0 97 18 0 24 0100100 0 0 0
>>> 0 0.00e+00 100 2.69e+02 0
>>> VecScatterEnd 100 1.0 4.9155e-02 2.5 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 0 0 0 0 0 20 0 0 0 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecCUDACopyTo 100 1.0 9.5078e-03 2.0 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 0 0 0 0 0 4 0 0 0 0 0 0
>>> 100 1.02e+02 0 0.00e+00 0
>>> VecCopyFromSome 100 1.0 2.8485e-02 1.4 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 0 0 0 0 0 14 0 0 0 0 0 0
>>> 0 0.00e+00 100 2.69e+02 0
>>>
>>> 6 MPI ranks + 6 GPUs + regular SF + No log_view
>>> MatMult: 100 1.0 1.4180e-01
>>> 399268
>>>
>>> 6 MPI ranks + 6 GPUs + CUDA-aware SF + log_view
>>> MatMult 100 1.0 1.1053e-01 1.0 9.66e+09 1.1 2.8e+03
>>> 2.2e+05 0.0e+00 1 99 97 18 0 100100100100 0 512224 642075
>>> 0 0.00e+00 0 0.00e+00 100
>>> VecScatterBegin 100 1.0 8.3418e-03 1.5 0.00e+00 0.0 2.8e+03
>>> 2.2e+05 0.0e+00 0 0 97 18 0 6 0100100 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterEnd 100 1.0 2.2619e-02 1.6 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 0 0 0 0 0 16 0 0 0 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>>
>>> 6 MPI ranks + 6 GPUs + CUDA-aware SF + No log_view
>>> MatMult: 100 1.0 9.8344e-02
>>> 575717
>>>
>>> 24 MPI ranks + 6 GPUs + regular SF + log_view
>>> MatMult 100 1.0 1.1572e-01 1.0 2.63e+09 1.2 1.9e+04
>>> 5.9e+04 0.0e+00 0 99 97 25 0 100100100100 0 489223 708601
>>> 100 4.61e+01 100 6.72e+01 100
>>> VecScatterBegin 100 1.0 2.0641e-02 2.0 0.00e+00 0.0 1.9e+04
>>> 5.9e+04 0.0e+00 0 0 97 25 0 13 0100100 0 0 0
>>> 0 0.00e+00 100 6.72e+01 0
>>> VecScatterEnd 100 1.0 6.8114e-02 5.6 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 0 0 0 0 0 38 0 0 0 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecCUDACopyTo 100 1.0 6.6646e-03 2.5 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 0 0 0 0 0 3 0 0 0 0 0 0
>>> 100 4.61e+01 0 0.00e+00 0
>>> VecCopyFromSome 100 1.0 1.0546e-02 1.7 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 0 0 0 0 0 7 0 0 0 0 0 0
>>> 0 0.00e+00 100 6.72e+01 0
>>>
>>> 24 MPI ranks + 6 GPUs + regular SF + No log_view
>>> MatMult: 100 1.0 9.8254e-02
>>> 576201
>>>
>>> 24 MPI ranks + 6 GPUs + CUDA-aware SF + log_view
>>> MatMult 100 1.0 1.1602e-01 1.0 2.63e+09 1.2 1.9e+04
>>> 5.9e+04 0.0e+00 1 99 97 25 0 100100100100 0 487956 707524
>>> 0 0.00e+00 0 0.00e+00 100
>>> VecScatterBegin 100 1.0 2.7088e-02 7.0 0.00e+00 0.0 1.9e+04
>>> 5.9e+04 0.0e+00 0 0 97 25 0 8 0100100 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>> VecScatterEnd 100 1.0 8.4262e-02 3.0 0.00e+00 0.0 0.0e+00
>>> 0.0e+00 0.0e+00 1 0 0 0 0 52 0 0 0 0 0 0
>>> 0 0.00e+00 0 0.00e+00 0
>>>
>>> 24 MPI ranks + 6 GPUs + CUDA-aware SF + No log_view
>>> MatMult: 100 1.0 1.0397e-01
>>> 544510
>>>
>>>
>>>
>>>
>>>
>>
>
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