# Building julia with \`march=native\`

**URL:** https://discourse.julialang.org/t/building-julia-with-march-native/82256
**Category:** General Usage
**Created:** [June 5, 2022, 2:07am UTC](https://discourse.julialang.org/t/building-julia-with-march-native/82256 "2022-06-05T02:07:21Z")
**Posts on this page:** 1
**Showing post:** 13

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### Author: ![stabbles](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stabbles/32/946_2.png) [@stabbles](https://discourse.julialang.org/u/stabbles)
#### Post date: [June 5, 2022, 11:39am UTC](https://discourse.julialang.org/t/building-julia-with-march-native/82256/13 "2022-06-05T11:39:51Z")

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@ImreSamu: regarding Clear Linux and the Phoronix benchmark, you have to take it with a grain of salt. For example they have amazing numbers for Zstd, but the reason is they set the default number of threads to 4, where other distro’s only use 1; the benchmark is builtin `zstd -b ...`, so it’s apples and oranges ([zstd benchmark misleading · Issue #633 · phoronix-test-suite/phoronix-test-suite · GitHub](https://github.com/phoronix-test-suite/phoronix-test-suite/issues/633)). Another issue is Phoronix compares Zstd 1.4 with 1.5, and there’s huge performance improvements between those releases, so it’s really not about Clear Linux being faster, but about them shipping a more recent version.

But sure, in some cases they get pretty good speedups, usually though about 5 - 10% thanks to PGO or LTO.

Getting PGO right is tricky, but I think this is the best type of optimization for large and branchy code bases like LLVM. I’ve spent some time enabling getting PGO to work in [the Spack package manager](https://github.com/spack/spack) for software stacks in general, and for Julia + LLVM things are really good.

Using `JULIA_LLVM_ARGS=-time-passes julia -O3 ./script.jl` where `script.jl` is pretty much `using LoopVectorization` with a `@turbo`’d inner product, compilation time drops by 25% for the most expensive LLVM passes:

```julia
[official binaries, generic, GCC, no PGO]:
   ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
   1.3508 ( 18.3%) 0.3359 ( 19.3%) 1.6867 ( 18.5%) 1.6809 ( 18.5%) X86 DAG->DAG Instruction Selection
   0.6616 ( 9.0%) 0.3140 ( 18.0%) 0.9756 ( 10.7%) 0.9732 ( 10.7%) X86 Assembly Printer
   0.3632 ( 4.9%) 0.0501 ( 2.9%) 0.4132 ( 4.5%) 0.4126 ( 4.5%) Greedy Register Allocator
   0.3423 ( 4.6%) 0.0511 ( 2.9%) 0.3934 ( 4.3%) 0.3904 ( 4.3%) Combine redundant instructions

[spack, generic, clang 14, no PGO]
   ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
   1.2367 ( 18.8%) 0.1931 ( 19.6%) 1.4299 ( 18.9%) 1.4298 ( 18.9%) X86 DAG->DAG Instruction Selection
   0.5216 ( 7.9%) 0.1528 ( 15.5%) 0.6744 ( 8.9%) 0.6744 ( 8.9%) X86 Assembly Printer
   0.3438 ( 5.2%) 0.0281 ( 2.9%) 0.3719 ( 4.9%) 0.3718 ( 4.9%) Greedy Register Allocator
   0.3196 ( 4.8%) 0.0333 ( 3.4%) 0.3529 ( 4.7%) 0.3525 ( 4.7%) Combine redundant instructions
   
[spack, generic, clang 14, PGO]:
   ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
   0.9713 ( 17.9%) 0.1708 ( 19.8%) 1.1421 ( 18.2%) 1.1421 ( 18.2%) X86 DAG->DAG Instruction Selection
   0.5047 ( 9.3%) 0.1283 ( 14.9%) 0.6329 ( 10.1%) 0.6329 ( 10.1%) X86 Assembly Printer
   0.3070 ( 5.7%) 0.0325 ( 3.8%) 0.3395 ( 5.4%) 0.3395 ( 5.4%) Greedy Register Allocator
   0.2403 ( 4.4%) 0.0340 ( 3.9%) 0.2743 ( 4.4%) 0.2741 ( 4.4%) Post RA top-down list latency scheduler

```

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