Background: For the majority of scripts, the fastest execution speed has been limited either by the built-in delays in some library functions, or by how the sim throttles the rate at which event handlers are triggered. That's the case anyway when the processing inside an event hander gets done faster than the rate at which the sim allows that event handler to be triggered. For example, after the Mono deployment, scripts still receive no more than 22 timer(), touch(), or sensor() events per second, and no more than about a dozen listen() events per second, just like before. Scripts like this will appear to run at the same speed as before.

However, if a script executes a relatively long sustained loop of code in a single invocation of an event handler, so that the time spent inside any one invocation of the event handler is much longer than the usual time between event triggers, and if delayed library calls are not used, then the upper limit on execution speed becomes dependent on the speed of the in-line LSL code, operators, casts, control structures, function calls, and all other core language features used. Those are much slower now.

This is a little surprising because we had thought that the LSL compiler option in Mono-enabled regions would continue generating the same byte code and we thought the LSL VM back end run time would continue running the byte code in the same way. But some timing measurements show that that's not the case – LSL statements run slower when recompiled by the LSL compiler in a Mono region.

A few examples:

• Every function call overhead is now more than twice what it used to be (0.88 ms/call, was 0.33 ms/call)

• Most math operators are less than half as fast as before: the statement vector v = <PI,PI,PI> + <PI,PI,PI> * PI; now takes 1.1 ms to execute, was 0.43 ms.

• Most non-delayed LSL library calls take twice as long to execute: llGetInventoryName() now takes 1.4 ms to execute, was 0.52 ms. llGetPos() takes 1.05 ms now, used to take 0.44 ms.

More documentation of the raw timing data is at http://wiki.secondlife.com/wiki/User:Becky_Pippen#LSL_Timings_and_Rates .