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Thread: speaking of multi-threading, last

9 Discord messages from ℹ️ - Information/general/threads/speaking-of-multi-threading-last.md.

Category: ℹ️ - Information Parent channel: #general Thread ID: 1490920503991337082

Messages: 9

message-1490971812601794692

2026-04-07T07:09:41.041+00:00 — Leo Moser (mole99) (@mole99)

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Content

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message-1490971821263294586

2026-04-07T07:09:43.106+00:00 — Leo Moser (mole99) (@mole99)

Content

Would you be willing to open an issue, or perhaps even contribute to LibreLane?

If enabling certain options would provide some speed improvements, that would definitely be appreciated. At first glance, I didn't see anything obvious in [Gate Resizer](https://openroad.readthedocs.io/en/latest/main/src/rsz/README.html).
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message-1491096947992559652

2026-04-07T15:26:55.643+00:00 — BreakingTaps (@polyfractal)

Content

ahhh sorry, that's what I get for responding without looking at my code changes.

I meant OpenSTA not resizer, my bad! I can disentangle the change from the rest of my stuff and send a PR, was a minor tweak to openroad.py in the OpenSTAStep.

(also added a blanket thread parameter since it looked like some other steps could take threads but I don't think that had much effect and is probably not very principled. Might have been redundant too)
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message-1491134544697364631

2026-04-07T17:56:19.396+00:00 — Leo Moser (mole99) (@mole99)

Content

Right! Yes, OpenSTA added native multithreading in its recent 3.0 release afaik.

Donn added [a compatibility layer](https://github.com/librelane/librelane/pull/881) to LibreLane, so we can continue using the same scripts for the LibreLane 3.0 release.

Currently, LibreLane spawns an OpenSTA process for each corner using the [MultiCornerSTA](https://github.com/librelane/librelane/blob/b1095babdafd1d0ceb8182b39a2485989903a81c/librelane/steps/openroad.py#L710) class.
This was great at the time and definitely better than running each corner sequentially ^^
However, if you only have three corners, like on gf180mcu, there isn't much to be gained.

Doing multithreading directly in OpenSTA is a major improvement, as many more threads can probably be used in parallel this way. It also means that we only need to keep the database in memory once, reducing the memory footprint and (likely) increasing cache hits. So running OpenSTA multithreaded is definitely desired :)
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message-1491134768006566139

2026-04-07T17:57:12.637+00:00 — Leo Moser (mole99) (@mole99)

Content

How did you modify LibreLane to run OpenSTA multithreaded? You should probably make sure that OpenSTA is only spawned once. Otherwise, you could end up with more software threads than hardware threads.
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message-1491134878035476520

2026-04-07T17:57:38.87+00:00 — Leo Moser (mole99) (@mole99)

Content

By default, each step should try to use up to `--jobs` threads if possible. This is done [here](https://github.com/librelane/librelane/blob/b1095babdafd1d0ceb8182b39a2485989903a81c/librelane/steps/klayout.py#L512), for example. As you can see, each step should also have local overrides e.g. in case running DRC with all available threads exhausts the system memory.
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message-1491478334406791248

2026-04-08T16:42:25.25+00:00 — BreakingTaps (@polyfractal)

Content

ahh good to know! I was only running small tests, will rerun with my full design to see if I accidentally blow up the machine 🙂

> How did you modify LibreLane to run OpenSTA multithreaded?

IIRC I was just passing in `-threads` when invoking OpenSTA process. It was a very small / targeted change
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message-1491478409988018336

2026-04-08T16:42:43.27+00:00 — BreakingTaps (@polyfractal)

Content

will doublecheck when i get home
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message-1491699940169220118

2026-04-09T07:23:00.181+00:00 — Leo Moser (mole99) (@mole99)

Content

Haha, it won't blow up the machine, but it could potentially slow things down because of all the context switching 😁

Good to know that's all that's needed. So, we just need to disable the explicit multiprocessing in LibreLane and enable `-threads`.
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