Monday, 28 December 2009

Reflections on Optimisation – Part 2, Existing Frameworks

Yesterday I introduced some topics on reflection performance, and investigated briefly the options to model abstraction, concluding that an abstract base-class / concrete subclass was a reasonable approach.

At this point, you could ask “so?” – the point is that I need a pretty optimised way of getting / setting data. So how about existing frameworks? Raw reflection? (PropertyInfo) ComponentModel? (PropertyDescriptor) HyperDescriptor? Let’s compare these options. I’ve setup a deliberately basic test rig, that simply tests each of these in a tight loop (again, deliberately avoiding boxing etc). As before, I’ll post the full code at the end of the series, but here’s the crude comparison:

Implementation Get performance Set performance
  • No wrapper (baseline)
  • Base class
  • HyperDescriptor
  • PropertyDescriptor*
  • PropertyInfo*
19, 37, 42, 79, 131 38, 55, 80, 131, 148
(numbers scaled, based on 750M iterations, except “*”; lower is better)

You might think “hey, PropertyInfo / PropertyDescriptor” aren’t too bad! Except for the *, which means that in order to get them into the same scale I had to introduce the line:

            count /= 100;

Where "count" is the number of iterations to perform. And even with this they are at the bottom of the table (by quite a margin). Yup – they really are over 100 times slower, which is why we need to optimise in the first place!

You might also conclude “HyperDescriptor doesn’t do too badly – just use that and move on”. Which would be valid in most cases (I’m pretty happy with that code, especially since that was my first foray into IL), except:

  • It wouldn’t let me investigate field vs property, polymorphism, and the other common “is this faster” questions I mentioned in part 1
  • It relies on constructs that don’t exist in CF / Silverlight, and which it would not be useful to duplicate (yet I need this for protobuf-net)
  • Sometimes the extra crank of the optimisation handle matters

Summary

In this discussion, I hope I’ve demonstrated that there really is a problem just using PropertyInfo etc, that we can overcome (evidence: HyperDescriptor), but we would hope to do so in a simplified, minimal way that can be modelled (perhaps with slightly different implementations) on all the common frameworks.

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