How startup works in Nelua execution process

[stefanos82]

I have noticed the following behavior: when I delete nelua_cache to force Nelua to regenerate the native code, its startup speed delays quite a lot.

On recompiling other sources, the startup speed drops but usually remains around 30 to 40 milliseconds approximately, give or take depending on the situation; the screenshot below is an exception though due to the nature of the code.

My question is, what does it cause the delay?

Is it compiler's cold startup on first execution?

[edubart]

The compiler startup just load lua files, and check some disk files. What you are experience is probably something related to your OS, when you delete the folder probably the OS is invalidating files cache and when you startup again the OS need to recache the files. You could confirm this executing the following:

sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"

For instance once the OS cache Nelua files, the startup takes about 20ms here, but when I drop the caches it takes more than 100ms:

➜  nelua-lang git:(master ✓) nelua -tb --no-cache examples/helloworld.nelua 
startup      22.6 ms
parse        1.5 ms
preprocess   0.0 ms
analyze      3.1 ms
generate     0.1 ms
compile      34.1 ms
total build  61.4 ms
➜  nelua-lang git:(master ✓) sync; sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"
➜  nelua-lang git:(master ✓) nelua -tb --no-cache examples/helloworld.nelua 
startup      132.1 ms
parse        5.6 ms
preprocess   0.1 ms
analyze      12.0 ms
generate     0.5 ms
compile      134.9 ms
total build  285.1 ms
➜  nelua-lang git:(master ✓) nelua -tb --no-cache examples/helloworld.nelua 
startup      22.2 ms
parse        1.5 ms
preprocess   0.0 ms
analyze      3.3 ms
generate     0.1 ms
compile      34.7 ms
total build  61.8 ms

Notice that after dropping the OS cache Nelua takes about 4x time to compile. When the OS decides to drop caches I can't say, this vary between setups, environment and activity, this is something specific to your OS and out of the scope here. You could use high speed hard disk or even put Nelua and all its files in RAM memory to speedup.

[stefanos82]

The interesting part of the output is the dual call for each Lua file; I really wonder why...

[edubart]

The interesting part of the output is the dual call for each Lua file; I really wonder why...

Probably the first open is just to check if the file exists, and the second the actual read.

[stefanos82]

I see...by the way, since the change in 1227c73, the whole build and execute procedure improved exponentially.

Now I get times like 25ms and such!

[edubart]

I see...by the way, since the change in 1227c73, the whole build and execute procedure improved exponentially.

Now I get times like 25ms and such!

That commit just changed a file system directory, so looks like to really be something related with OS/disk/file caching.

[stefanos82]

The thing is, if you deleted nelua_cache and re-executed the same code, the startup time never dropped this low before the default cache directory.

It's really incredible to be honest with you!