updating docs to include matrix-vector multiply example

[akashkgarg]

As I work through how to speed-up some of functionality in the SciML codebases using multiple GPUs, I thought I'd add my small experiments as examples for other users of this package. Comments/feedback is welcome if the example(s) shown could be done better.

[codecov[bot]]

Codecov Report

Merging #918 (03192b6) into master (eb7c326) will decrease coverage by 0.00%. The diff coverage is n/a.

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- Coverage   77.00%   76.99%   -0.01%     
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+ Hits         5934     5935       +1     
- Misses       1772     1773       +1     

Impacted Files	Coverage Δ
lib/cusolver/CUSOLVER.jl	82.00% <0.00%> (-1.34%)	:arrow_down:

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[maleadt]

Nice example! Any idea why the minimum times show a much more pronounced speed-up? It could be because CUDA.@sync does a synchronize(), so only synchronizes the current task. Maybe it should call device_synchronize() instead, but that's fairly costly.

[akashkgarg]

@maleadt great question. I added device_synchronize() and it does reduce the variance quite a bit. The updated is probably a more reasonable implementation/benchmark.

[akashkgarg]

@maleadt I added another example that does a reduction over a large array. Surprisingly, the multiple GPU case is significantly slower (although the maximum time is about 1/3 the single GPU case). Perhaps there is a better way to partition the data/computation than I'm doing here?

[amontoison]

Nice examples !