[Users] Benchmarking results for McLachlan rewrite

[Ian Hinder]

On 24 Jul 2015, at 19:15, Erik Schnetter <schnetter at cct.lsu.edu> wrote:

> On Fri, Jul 24, 2015 at 11:57 AM, Ian Hinder <ian.hinder at aei.mpg.de> wrote:
> 
> On 8 Jul 2015, at 16:53, Ian Hinder <ian.hinder at aei.mpg.de> wrote:
> 
>> 
>> 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.
> 
> I have now run my benchmarks on both the original and the rewritten McLachlan.  I seem to find that the ML_BSSN_* functions in
> Evolve/CallEvol/CCTK_EVOL/CallFunction/thorns, excluding the constraint calculations, are between 11% and 15% slower with the rewrite branch, depending on the details of the evolution.  See attached plot.  This is on Datura with quite old CPUs (Intel Xeon CPU X5650 2.67GHz).
> 
> What exactly do you measure -- which bins or routines? Does this involve communication? Are you using thorn Dissipation?


I take all the timers in Evolve/CallEvol/CCTK_EVOL/CallFunction/thorns that start with ML_BSSN_ and eliminate the ones containing "constraints" (case insensitive).  This is running on two processes, one node, 6 threads per node.  Threads are correctly bound to cores.  There is ghostzone exchange between the processes, so yes, there is communication in the ML_BSSN_SelectBCs SYNC calls, but it is node-local.  

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

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