[Users] Benchmarking results for McLachlan rewrite

[Ian Hinder]

On 8 Jul 2015, at 15:14, Erik Schnetter <schnetter at cct.lsu.edu> wrote:

> I added a second benchmark, using a Thornburg04 patch system, 8th order finite differencing, and 4th order patch interpolation. The results are
> 
> original: 8.53935e-06 sec
> rewrite:  8.55188e-06 sec
> 
> this time with 1 thread per MPI process, since that was most efficient in both cases. Most of the time is spent in inter-patch interpolation, which is much more expensive than in a "regular" case since this benchmark is run on a single node and hence with very small grids.
> 
> With these numbers under our belt, can we merge the rewrite branch?

The "jacobian" benchmark that I gave you was still a pure kernel benchmark, involving no interpatch interpolation.  It just measured the speed of the RHSs when Jacobians were included.  I would also not use a single-threaded benchmark with very small grid sizes; this might have been fastest in this artificial case, but in practice I don't think we would use that configuration.  The benchmark you have now run seems to be more of a "complete system" benchmark, which is useful, but different.

I think it is important that the kernel itself has not gotten slower, even if the kernel is not currently a major contributor to runtime.  We specifically split out the advection derivatives because they made the code with 8th order and Jacobians a fair bit slower.  I would just like to see that this is not still the case with the new version, which has changed the way this is handled.



> 
> -erik
> 
> 
> On Sat, Jul 4, 2015 at 5:19 PM, Ian Hinder <ian.hinder at aei.mpg.de> wrote:
> hi Erik,
> 
> You could try the ones at
> 
> https://bitbucket.org/ianhinder/cactusbench/src/faea4e13ed4232968e81edd1bbc80519198fe2b2/examples/ML_BSSN_Test/benchmark/?at=master
> 
> I haven't updated them in a while, but hopefully the ET is sufficiently backward compatible for them to still work.
> 
> -- 
> Ian Hinder
> http://members.aei.mpg.de/ianhin
> 
> On 4 Jul 2015, at 17:04, Erik Schnetter <schnetter at cct.lsu.edu> wrote:
> 
>> On Sat, Jul 4, 2015 at 10:21 AM, Ian Hinder <ian.hinder at aei.mpg.de> wrote:
>> 
>> On 3 Jul 2015, at 22:38, Erik Schnetter <schnetter at cct.lsu.edu> wrote:
>> 
>>> I ran the Simfactory benchmark for ML_BSSN on both the current version and the "rewrite" branch to see whether this branch is ready for production use. I ran this benchmark on a single node of Shelob at LSU. In both cases, using 2 OpenMP threads and 8 MPI processes per node was fastest, so I am reporting these results below. Since I was interested in the performance of McLachlan, this is a unigrid vacuum benchmark using fourth order differencing.
>>> 
>>> One noteworthy difference is that dissipation as implemented in the "rewrite" branch is finally approximately as fast as thorn Dissipation, and I have thus used this option for the "rewrite" branch.
>>> 
>>> Here are the high-level results:
>>> 
>>> current: 3.03136e-06 sec per grid point
>>> rewrite: 2.85734e-06 sec per grid point
>>> 
>>> That is, the rewrite branch is about 5% faster.
>> 
>> Hi Erik,
>> 
>> That is very reassuring!  However, for production use, I would be more interested in 6th or 8th order finite differencing (where the advection stencils become very large), and with Jacobians.  If 8th order with Jacobians is at least a similar speed with the rewrite branch, then I would be happy with switching.
>> 
>> Ian
>> 
>> Do you want to suggest a particular benchmark parameter file?
>> 
>> -erik
>> 
>> -- 
>> Erik Schnetter <schnetter at cct.lsu.edu>
>> http://www.perimeterinstitute.ca/personal/eschnetter/
> 
> 
> 
> -- 
> Erik Schnetter <schnetter at cct.lsu.edu>
> http://www.perimeterinstitute.ca/personal/eschnetter/

-- 
Ian Hinder
http://members.aei.mpg.de/ianhin

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