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- Subject: Re: How fast is LuaJIT supposed to be?
- From: Axel Kittenberger <axkibe@...>
- Date: Sat, 22 Jan 2011 09:48:42 +0100
as usual when optimizing for speed, you just code naive, then profile
and optimizie only the 5% that use 95% of performance.
In your sieve this was very likely "canditate" a variable which is
used a lot in every innerst loop.
On Sat, Jan 22, 2011 at 7:34 AM, Steve Litt <firstname.lastname@example.org> wrote:
> On Friday 21 January 2011 14:34:24 Axel Kittenberger wrote:
>> On Fri, Jan 21, 2011 at 8:10 PM, Alexander Gladysh <email@example.com>
>> > On Fri, Jan 21, 2011 at 22:08, Steve Litt <firstname.lastname@example.org>
>> >> On Friday 21 January 2011 03:48:02 Axel Kittenberger wrote:
>> >>> Ah, a sieve of eratosthenes (there are various ways to get primes). I
>> >>> suppose you will find a considerable perfomance increase (native and
>> >>> jit) if you use "candidate" as a local variable you pass as argument
>> >>> and return value to find_next_candidate() instead of storing it as
>> >>> "candidate" key in the prime array.
>> >> Is table lookup really more expensive than passing in as an arg and
>> >> passing back as a return? Ugh!
>> > Try LJ2, you will think about these implementation details no longer. :-)
>> Strange I didnt see that email :-/
>> Lua Tables are hashtables. Putting and getting stuff from a hashtable
>> is of course slower than from a local variable (that is either on
>> stack or even a register)
> How much slower? To my way of thinking, tables of key/value pairs are the
> heart and soul of Lua. I'd hate to start worrying about speed when using them.
> Steve Litt
> Recession Relief Package
> Twitter: http://www.twitter.com/stevelitt