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0 pointsmaxime_cb8mo ago0 comments

Instigator of YJIT, the CRuby JIT here.

It's easy to dismiss our efforts, but Ruby is just as dynamic if not more than Python. It's also a very difficult language to optimize. I think we could have done the same for Python. In fact the Python JIT people reached out to me when they were starting this project. They probably felt encouraged seeing our success. However they decided to ignore my advice and go with their own unproven approach.

This is probably going to be an unpopular take but building a good JIT compiler is hard and leadership matters. I started the YJIT project with 10+ years of JIT compiler experience and a team of skilled engineers, whereas AFAIK the Python JIT project was lead by a student. It was an uphill battle getting YJIT to work well at first. We needed grit and I pushed for a very data-driven approach so we could learn from our early failures and make informed decisions. Make of that what you will.

Yes Python is hard to optimize. I Still believe that a good JIT for CPython is very possible but it needs to be done right. Hire me if you want that done :)

Several talks about YJIT on YouTube for those who want to know more: https://youtu.be/X0JRhh8w_4I

0 comments

kenjin40968mo ago

Hey Maxime!

> whereas AFAIK the Python JIT project was lead by a student.

I am definitely not leading the team! I am frankly unqualified to do so lol. The team is mostly led by Mark Shannon, who has 10+ years of compiler/static analysis experience as well. The only thing I initially led was the optimizer implementation for the JIT. The overall design to choose tracing, to use copy and patch, etc. were other people.

> However they decided to ignore my advice and go with their own unproven approach.

Your advice was very much appreciated and I definitely didn't ignore your advice. I just don't have much say over the initial architectural choices we make. We're slowly changing the JIT based on data, but it is an uphill battle like you said. If you're interested, it's slowly becoming more like lazy basic block versioning https://github.com/python/cpython/issues/128939

You did great work on YJIT, and I am quite thankful for that.

maxime_cbOP8mo ago

Thanks Ken. Apologies if I misunderstood the situation. I wish you all the best.

ecshafer8mo ago

Thanks for the response Maxime, your work on YJIT is astounding. The speedup from YJIT was a huge improvement over cRuby or MJIT, and the work was done relatively quickly compared to Python which seems to always be talking about this JIT but we are never seeing a comparable release.

josalhor8mo ago

Having had no experience in JIT development but having followed the faster cpython JIT progress on a weekly basis, I do find their JIT strategy a bit weird. The entire decision seemed to revolve around not wanting to embebed an external JIT/compiler with all that entails...

At first I thought their solution was really elegant. I have an appreciation for their approach, and I could have been captivated myself to choose it. But at this point I think this is a sunk cost fallacy. The JIT is not close to providing significant improvements and no one in the faster cpython community seems to be able to call the shot that the foundational approach may not be able to give optimal results.

I either hope to be wrong or hope that faster cpython managment has a better vision for the JIT than I do.

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