1509314 - Investigate using LLVM propeller to improve code layout for improved cache locality and branch prediction

Status: NEW

(Firefox Build System :: Toolchains, enhancement, P3)

Description

[Mayank Bansal]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0

Steps to reproduce:

Investigate if its feasible to use BOLT optimizer from facebook incubator

https://github.com/facebookincubator/BOLT

This found mention in https://docs.google.com/presentation/d/1vJrsJ7fRSi6uidJWVSI2bg8aR19gXeshLgD0tcXfMqg/edit#slide=id.g46ee6ad94d_5_35

Comment 1

[Mike Hommey [:glandium]]

I'm not particularly convinced it's worth investigating for Firefox, for 2 reasons:

• it's not cross-platform (it's pretty much Linux only)
• even if we did use it, it wouldn't be used in downstream Linux distributions.

OTOH, AIUI, people in the LLVM community have shown interest in integrating something similar to BOLT in LLVM, which makes sense: there's nothing in BOLT that couldn't be done with PGO+LTO.

Comment 2

[Mayank Bansal]

https://github.com/google/llvm-propeller/

http://lists.llvm.org/pipermail/llvm-dev/2019-September/135393.html

Google's implementation of BOLT as part of LLVM

Comment 3

[Mayank Bansal]

Google Propeller is getting upstreamed:
https://www.phoronix.com/scan.php?page=news_item&px=Google-Propeller-Some-Upstream

Comment 4

[(Away)]

AIUI, Propeller is still Linux-only due to the reliance on perf data.

Comment 5

[Mayank Bansal]

FWIW, Facebook's BOLT is merged in LLVM

Comment 6

[Mayank Bansal]

Looks like AutoFDO and propeller are merged into the kernel now : https://www.phoronix.com/news/AutoFDO-Propeller-Linux-6.13

Comment 7

[Mayank Bansal]

https://discourse.llvm.org/t/rfc-upstreaming-propeller-profile-conversion-tool/89173
Upstreaming Propeller Profile Conversion Tool