Lua Performance

Overview

This page is copied from the CA wiki. The widget used in the performance tests is available from the CA SVN.

Other Considerations

It is a well known axiom in computing that

"We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil"

- Donald Knuth

Lua coders should keep that in mind, and especially when visiting this page. Readability and maintainability are in most cases just as important, and optimizing code for every last ounce of performance can severely impact those qualities. On the other hand, some of the optimizations suggested have little bearing on readability and should generally always be applied, e.g. localization of API functions, or actually make for neater code e.g. the use of or rather than a nil-check. Generally speaking, optimize only once you are sure that there is or will be a performance bottleneck.

Performance Tests

TEST 1: Localize

Code:

  local min = math.min

Results:

Non-local: 0.719 (158%)

Localized: 0.453 (100%)

Conclusion:

Yes, we should localize all standard lua and Spring API functions.

TEST 2: Localized Class-Methods (with only 3 accesses!)

Code 1:

  for i=1,1000000 do
    local x = class.test()
    local y = class.test()
    local z = class.test()
  end

Code 2:

  for i=1,1000000 do
    local test = class.test
    local x = test()
    local y = test()
    local z = test()
  end

Results:

Normal way: 1.203 (102%)

Localized: 1.172 (100%)

Conclusion:

No, it isn't faster to localize a class method IN the function call.

TEST 3: Unpack A Table

Code 1:

  for i=1,1000000 do
    local x = min( a[1],a[2],a[3],a[4] )
  end

Code 2:

  local unpack = unpack
  for i=1,1000000 do
    local x = min( unpack(a) )
  end

Code 3:

  local function unpack4(a)
    return a[1],a[2],a[3],a[4]
  end
  for i=1,1000000 do
    local x = min( unpack4(a) )
  end

Results:

with [ ]: 0.485 (100%)

unpack(): 1.093 (225%)

custom unpack4: 0.641 (131%)

Conclusion:

Don't use unpack() in time critical code!

TEST 4: Determine Maximum And Set It ('>' vs. max)

Code1:

  local max = math.max
  for i=1,1000000 do
     x = max(random(cnt),x)
  end

Code2:

  for i=1,1000000 do
    local r = random(cnt)
    if (r>x) then x = r end
  end

Results:

math.max: 0.437 (156%)

'if > then': 0.282 (100%)

Conclusion:

Don't use math.[max|min]() in time critical code!