Storing state information (was Re: Ah, those uninitiated people...)

[Mark Hamburg <mark@...>]

On Jan 14, 2010, at 7:15 AM, Mark Hamburg wrote:

> While upvalues are slower than locals, I suspect that a table lookup is slower still.

Some statistics. This basically is the result of timing a loop that counts up to a really big number using various ways of storing the counter.

Lua 5.1.4:
	Local	                     98.276374
	Upvalue (open)      209.396356
	Upvalue	(closed)    216.251567
	Table field                561.369677
	Global			   612.179566

So, locals are a clear win. I'm interested that tables are a win relative to globals. Presumably this has to do with the table being smaller. Or else there's a lot of overhead in the opcodes to get and set globals.

LuaJIT levels the playing field.

LuaJIT 2.0:
	Local                      11.21
	Upvalue (open)    11.31
	Upvalue (closed) 11.18
	Table field		11.15
	Global			11.36

Lua 5.2 (work1) is also definitely a bit slower:

Lua 5.2 (work1):
	Local	                  107.266672
	Upvalue (open)      223.447284
	Upvalue	(closed)    222.159344
	Table field                620.652007
	Global			   677.802486

Mark