Re: Allocation sinking in git HEAD
- From: Coda Highland <chighland@xxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Tue, 3 Jul 2012 07:50:19 -0500
On Tue, Jul 3, 2012 at 7:21 AM, Mike Pall <mike-1207@xxxxxxxxxx> wrote:
> LuaJIT git HEAD now contains the new allocation sinking and store
> sinking optimization.
>
> This optimization is enabled by default. In case you encounter any
> problems and want to check whether they are caused by this
> optimization, you can turn it off with: -O-sink
>
> The optimization is geared towards the elimination of short-lived
> aggregates. It handles plain Lua tables as well as FFI cdata (e.g.
> structs, complex or short arrays). It also handles elimination of
> immutable FFI types that are implicitly boxed (e.g. 64 bit ints or
> pointers) in more contexts (e.g. loop-carried variables).
>
> This optimization adds quite a bit of complexity, so I'd appreciate
> it if it would receive wider testing. Feedback welcome!
>
> Here are a few examples that show the improved performance. The
> timings in seconds are for Lua 5.1.5 vs. LuaJIT git HEAD on x86
> (32 bit). Lower numbers are better:
>
> Typical point class with Lua tables:
>
> local point
> point = {
> new = function(self, x, y)
> return setmetatable({x=x, y=y}, self)
> end,
> __add = function(a, b)
> return point:new(a.x + b.x, a.y + b.y)
> end,
> }
> point.__index = point
> local a, b = point:new(1.5, 2.5), point:new(3.25, 4.75)
> for i=1,1e8 do a = (a + b) + b end
> print(a.x, a.y)
>
> 140.0 Lua
> 26.9 LuaJIT -O-sink
> 0.35 LuaJIT -O+sink *** 400x faster than Lua ***
>
> Typical point class with cdata struct:
>
> local ffi = require("ffi")
> local point
> point = ffi.metatype("struct { double x, y; }", {
> __add = function(a, b)
> return point(a.x + b.x, a.y + b.y)
> end
> })
> local a, b = point(1.5, 2.5), point(3.25, 4.75)
> for i=1,1e8 do a = (a + b) + b end
> print(a.x, a.y)
>
> 10.9 LuaJIT -O-sink
> 0.20 LuaJIT -O+sink *** 700x faster than Lua ***
>
> 64 bit arithmetic in a loop:
>
> local x = 0LL
> for i=1,1e9 do x = x + 100 end
> print(x)
>
> 45.8 LuaJIT -O-sink (x86)
> 40.9 LuaJIT -O-sink (x64)
> 0.84 LuaJIT -O+sink (x86)
> 0.48 LuaJIT -O+sink (x64)
>
> --Mike
>
Very impressive. :) It's performance improvements like this that make
me wish I could use LuaJIT at work!
/s/ Adam
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