not planned Switch to LuaJIT to improve performance

[TheXerxes]

DCS is still utilizing Lua 5.1, which is both unsupported and obsolete. Alternatives such as LuaJIT and Luau offer drop-in replacement compatibility with the Lua 5.1 API and present significant advantages.

LuaJIT, in particular, stands out due to its remarkable performance, which you can evaluate in the provided benchmark at this link:

https://eklausmeier.wordpress.com/2020/05/14/performance-comparison-pallene-vs-lua-5-1-5-2-5-3-5-4-vs-c/

. LuaJIT is about 19 times faster than Lua 5.1 in the provided benchmark. LuaJIT elevates performance by compiling Lua code directly into machine code during runtime, bypassing the virtual machine (VM) approach inherent to Lua 5.1. This can lead to execution speeds on par with C and C++ in certain scenarios.

Additionally, LuaJIT enhances Foreign Function Interface (FFI) calls, which could notably optimize the interactions between C++ and Lua within your project. Given these points, I strongly suggest transitioning to LuaJIT or Luau to modernize and boost DCS's runtime efficiency. This change is likely to yield a significant improvement in both frame rates and server mission performance without breaking compatibility with the available Lua code base.

Best Regards,

Xerxes of Shadow Reapers

[-Cipher-]

I just checked the benchmark and that was a significant boost, I am not a skilled coder nor a developer but based on my observation on this if DCS codes could be upgraded without major compatibility problems I believe it could take it to the next level so yeah a +1 from me.

 

[Raven (Elysian Angel)]

Perhaps it's a good idea to send it as a PM to Bignewy or NineLine (or SkateZilla), and ask what they think about it?

[cfrag]

16 minutes ago, Insonia said:

Most DCS lua just tables.

And Mission Editor.

Indeed it does not seem as if there is a great appetite in ED to change the mission scripting environment, since it apparently runs good enough, and there is very little obvious return on investment for funds invested in upgrading Lua (interpreted) to Lua (JIT) - which I imagine to be very different from a drop-in replacement (read: expensive in terms of effort). 

Hopefully I'm wrong, as compiled Lua - even if JIT - sounds like a nice performance boost.

[SkateZilla]

5 hours ago, Raven (Elysian Angel) said:

Perhaps it's a good idea to send it as a PM to Bignewy or NineLine (or SkateZilla), and ask what they think about it?

My thoughts and opinions are of my own, and have no affiliation w/ ED or their Business decisions.

But I did give it a re-post.

[Raven (Elysian Angel)]

1 hour ago, SkateZilla said:

My thoughts and opinions are of my own

Yes, exactly! You have the know-how and you're an independent voice who has contacts with ED. That's all I meant with my suggestion  

[TheXerxes]

To clarify, the original Lua project (found at lua.org) and LuaJIT (available at luajit.org) are distinct projects. LuaJIT enhances Lua 5.1 compatibility by offering substantial performance improvements, both with and without its Just-In-Time compilation features, compared to the standard Lua 5.1 implementation. Assuming that a system like DCS relies heavily on Lua's table structures, which are dependent on Lua's hashing functions and internal mechanisms, a switch to LuaJIT would lead to more efficient table access. This is because LuaJIT not only compiles the code for reading tables, resulting in smoother linear execution but also employs a more efficient and better-distributed hashing algorithm (https://en.wikipedia.org/wiki/Hash_function).

Regardless of whether DCS utilizes Lua solely for its hash tables, which it doesn't, LuaJIT has the capacity to speed up both the lexing/parsing phase—which translates the program's text into a form the computer can process—and the performance of table operations.

It is important to mention LuaJIT's performance in calling C and C++ functions is better than Lua 5.1 too, so switching to it will boost communication with DLLs and compiled part of DCS.

The best thing is that LuaJIT is C API compatible with Lua 5.1 C API, so it is possible to use it as a drop-in replacement in DCS with some small changes.

The other positive point is that LuaJIT is well battle-tested, companies and organizations like Cern, Cloudflare, and Cisco are notable users of it.

I would love to hear from the DCS development team.

[BIGNEWY]

Hi all, 

we do have an internal report to investigate the potential of LuaJIT. I have marked this thread investigating for now

thank you

[BIGNEWY]

Hi all, 

we have tried LuaJIT but DCS does not work with LuaJIT out of the box and requires heavy debugging and an unknown number of fixes, It also messes with the function of some 3rd party modules. At this stage it would be a lot of work to change, so for now it is not planned. 

thank you

[Raven (Elysian Angel)]

That's a shame... Thanks for checking anyway  

[Kappa-131st]

On 6/12/2024 at 10:14 AM, BIGNEWY said:

Hi all, 

we have tried LuaJIT but DCS does not work with LuaJIT out of the box and requires heavy debugging and an unknown number of fixes, It also messes with the function of some 3rd party modules. At this stage it would be a lot of work to change, so for now it is not planned. 

thank you

Thanks for checking!

[cfrag]

On 6/12/2024 at 10:14 AM, BIGNEWY said:

we have tried LuaJIT but DCS does not work with LuaJIT

This is sad news - but thank you so much for updating us. It's good to know that this milestone was reached, even if it did not yield the results that we have hoped for.