Thursday, September 17, 2009

Race to do nothing!

In the early days there was prelink as part of maemo. It disappeared in the n810 distribution ranges. I noticed that there is no armel deb in debian for prelink, but there were murmurs of folks hacking it to work. Push finally came to shove, and as I like C++ many of my apps on maemo have quite a few symbols that need to be resolved before the app can run.

The long story short, prelink_0.0.20090311 is up at my repo. Use at your own risk, if your device breaks you get to keep both pieces etc etc.

Initial benchmarking: for an app that uses a few libraries, is C++, and has quite a few symbols that the dynamic linker has to attend to. For a complete run before it was 5.2 seconds on a warm start, with prelink of the binary it is 2.5 seconds. Considering that in that 2.5 the app itself has to completely run, there was a huge amount of time spent, err wasted, in the dynamic linker.

Of course, if I can get hidden symbols to work too then that 2.5 might drop back to 1.5-2 seconds. But for hidden symbols you have to either wrap things in pragmas or declare each function and class as exposed or not, so for a large library its quite intrusive. But the prelink is a huge gain for no code changes, so far at least. YMMV.

It's a touch ironic that Nokia recommends using prelink for embedded devices. But that is for qtopia... maybe for the next distro prelink will reappear in the default installation.


Murray said...

Doesn't maemo-launcher achieve the same thing? The maemomm-booster module preloads the Hildon C++ bindings, for instance.

monkeyiq said...

OK, I just read up on this and made a ferris-booster. During initial testing the boosted binary appears about the same, total execution time wise as the prelinked one.

This is of course on the same short lived process. Of course, further testing might change the tides. But I suspect that the symbol resolution is larger than the actual "library init" code that is gained though a shared preinit() function.