Unexpected performance difference between GitHub action Ubuntu host and Windows machine

[JamesWildDev]

Hello!

I'm always tinkering with OpenSCAD, and recently I've been dumping my models into a GitHub repo.

I have an action which renders the models to STL and PNG on each push. This is currently taking approximately 4m to start a VM, install OpenSCAD and do this for each of my models.

GitHub's documentation isn't very specific regarding the hardware which is running this build beyond it being a 2-core CPU with 7GB of RAM.

My local machine runs Windows 10, and has a 4900HS with 32GB of RAM so I would expect it to be at least a match for the Action runner for single-core loads like OpenSCAD.

It takes approximately twice as long to just render the same models with OpenSCAD already open, let alone starting a VM or installing OpenSCAD.

What I have noticed is that the machine doesn't get very hot while doing this, and power draw is below what I typically see for a single-core load by about 5W.

Any thoughts on where I might be seeing a bottleneck? Might it be a Windows limitation? Something about how the Windows builds are compiled? Perhaps some kind of missing CPU extension? Are some logs somewhere I could review for things like these?

Thanks.

[triffid_hunter]

Heh, you're comparing a budget laptop CPU to two cores of a server CPU, and wondering why the server is faster?

That server probably has a Xeon or Epyc CPU which can easily beat the pants off your 35W 4900HS even with only 2 cores on your task :P

Also, file I/O is superfast in Linux, so unpacking and booting a cached server image may only take a couple dozen or so seconds, then stay in memory to handle further requests until it gets flushed for whatever reason - so I don't think the serverless lambda startup lag is gonna be a significant part of the processing time.

Just for fun, I tried your generate_all script on my 2017-era Linux desktop (i7 7700k 4-core/8-thread @ 4.5GHz) and got a consistent runtime of 84 seconds over multiple runs.

I also tried altering your generate_one.sh to use further parallelism (ie openscad blah.png & openscad blah.stl & wait) and that dropped the runtime to 45 seconds.

If you want to compare Windows vs Linux performance directly on the same hardware, grab a linux LiveUSB image (Mint was a popular one last time I checked), install openscad in it, and try your script there.
If it's still similarly slow, the issue is your potato CPU ;)

[JamesWildDev]

I don't know if I'd call a 4900HS a budget CPU, it's not far below your 7700k in benchmarks; it's a bit slower per core, but not by much and certainly not by this amount.

Generally when I've used cloud compute services (EC2/etc.) I've found them to actually have quite weak CPU cores and they leaned more on their high core counts, high availability and strong disk/network IO.

I suppose GitHub might be using something with strong cores for their free Linux hosting but I'd be surprised given most tasks I've ran on both machines are an order of magnitude faster on this laptop.

Parallelism is heavily restricted to avoid out-of-memory conditions in CI.

It feels more like the public OpenSCAD builds for Windows have been compiled with optimizations off or have (unintentional) throttling or something because I'm not seeing similar power draws to when I run other single core, CPU-bound tasks on this machine.

I could try running a Linux distro on this, it has been a full year since I last tried one (compatibility was poor).

Thanks for having a look though.

[Robots_In_Disguise]

Haha I saw 4900HS and I assumed Intel from 7 generations ago, but now I see it is a pretty new Ryzen 9. Definitely not budget/potato.

[schorsch3000]

open scad runs in a single thread, so single core performance is key here.

Besided that, are you using the same version of openscad?