Re: Trace compilation from embedded LuaJIT
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- Subject: Re: Trace compilation from embedded LuaJIT
- From: "Robert G. Jakabosky" <bobby@...>
- Date: Wed, 3 Aug 2011 16:46:51 -0700
On Wednesday 03, Douglas Creager wrote:
> Hi all,
>
> I have a quick question about how much hot JIT action you'll get when
> embedding LuaJIT within another application. My understanding is that
> LuaJIT's heuristics look for hot traces by identifying loops within the
> Lua code. But what happens if the loop is in the host C application? So
> for instance, I've got a data processing app where I'm allowing the user
> to do some custom processing by providing a Lua function. That's going to
> be a hot function, since I'm processing many many records, so I'd like to
> have that function trace-compiled down into machine code. [As an aside,
> this is a good use case for a possible lua_pushcdata function on the C
> side of things, to get a nice FFI cdata object into the Lua code from the
> host app. But I digress.]
>
> Are there any constructs that would let me accomplish this? In stock Lua
> I'd just call the user's customization function using lua_pcall, but then
> there's no Lua loop to cause LuaJIT to start recording traces.
>
> I've also tried using a coroutine, where I pass in each record using
> lua_resume:
>
> while true do
> local more, record = coroutine.yield()
> if not more then return end
> process(record)
> end
>
> This gives me a loop, which will be executed once per record. But
> unfortunately coroutine.yield is NYI, so I don't get a nice tasty compiled
> trace.
>
> Any other things I can try? Or is this too far outside of LuaJIT's
> intended use cases?
How about moving the data processing loop into Lua (for both the custom Lua
callbacks and any other C callbacks).
while true do
local record = get_next_record()
if not record then return end
-- call call all c/lua per-record callbacks
for i=1,#callbacks do
callbacks[i](record)
end
-- cleanup record
cleanup_record(record)
end
If you are worried about the speed when not using LuaJIT, then have another
version of that loop written in C.
--
Robert G. Jakabosky