[petsc-dev] Feed back on report on performance of vector operations on Summit requested

Smith, Barry F. bsmith at mcs.anl.gov
Tue Oct 29 16:09:14 CDT 2019


     Thanks for your feedback.

> On Oct 23, 2019, at 7:15 PM, Jed Brown <jed at jedbrown.org> wrote:
> IMO, Figures 2 and 7+ are more interesting when the x axis (vector size)
> is replaced by execution time.  

> We don't scale by fixing the resource
> and increasing the problem size, we choose the global problem size based
> on accuracy/model complexity and choose a Pareto tradeoff of execution
> time with efficiency (1/cost) to decide how many nodes to use.  Most of
> those sloping tails on the left become vertical lines under that
> transformation.

   I don't see the connection between your first sentence and the other sentences.

   How does the plot with time instead of size tell you what number of processors to use?

   I don't understand the plots with x as a time axis, so I suspect most potential readers won't. The only point of the plots is really to give an idea of the scale of the performance and that performance is low except for large sizes so will keep the plot axis as is.

> How is latency defined in Figure 6?

  Least squares. We will reference the definition given later.
> Data upon which the latency-bandwidth model is derived should be plotted
> to show the fit, and the model needs to be constrained to avoid negative
> latency.

   For the CPU we are playing with the plots to see if they can convey some useful information. The performance over each range of values on the CPU is simply not linear, hence a linear fit gives incomplete information. The negative latencies perhaps don't convey particularly useful information so we may not list them, the bandwidth value I think is still useful because it does convey locally the performance of the memory.

> If you give me access to the repository with data and current plotting
> scripts, I can take a crack at slicing it in the way that I think would
> be useful.

  Hannah will give you the data.


> "Smith, Barry F. via petsc-dev" <petsc-dev at mcs.anl.gov> writes:
>>   We've prepared a short report on the performance of vector operations on Summit and would appreciate any feed back including: inconsistencies, lack of clarity, incorrect notation or terminology, etc.
>>   Thanks
>>    Barry, Hannah, and Richard

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