Re: [OE-core] [PATCH] rust-llvm: Compile llvm to use dynamic libraries

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Mon, 2025-03-31 at 21:44 +0100, Richard Purdie via
lists.openembedded.org wrote:
> On Mon, 2025-03-31 at 15:08 -0400, Randy MacLeod wrote:
> >  
> > On 2025-03-31 12:13 p.m., Khem Raj via lists.openembedded.org
> > wrote:
> >  
> > > On Mon, Mar 31, 2025 at 6:30 AM Richard Purdie via
> > > lists.openembedded.org
> > > <richard.purdie=linuxfoundation.org@lists.openembedded.org>
> > > wrote:
> > > > Our main llvm recipe uses dynamic linking already but rust-llvm
> > > > does not.
> > > >  Enabling this significanly reduces the size of llvm-rust to
> > > > about a third
> > > >  of what it was, which is a bettter configuration for us
> > > > leading to smaller
> > > >  TMPDIR and sstate objects
> > > > 
> > >  
> > > 
> > >  
> > >  
> > > It will slow down the compiler execution and sometimes its could
> > > be significant as well we have seen this with clang so it would
> > > be good to have some idea around that least we provide a slow
> > > compiler compared to other distro infrastructures 
> > >  
> > >  
> > >  
> > >  
> >  
> > We'll get some performance info from the YP AB perf builds.
> 
> https://valkyrie.yocto.io/pub/non-release/20250331-105/testresults/buildperf-debian11/perf-debian12-vk_master-next_20250331181527_9ba5b4f4e4.html
> https://valkyrie.yocto.io/pub/non-release/20250331-104/testresults/buildperf-alma8/perf-alma8-vk_master-next_20250331181513_9ba5b4f4e4.html
> 
> The build time is fractionally faster (1%?) but hard to say within
> noise.
> 
> The diskspace drop is convincing, 2.3GB less TMPDIR size (2.3%).
> 
> The rm_work TMPDIR size also drops by 1GB (6%) which is particularly
> significant and nice to have.
> 
> In builds with rust-llvm as well as rust-llvm-native, this will
> double up for a double win.

The analysis is a bit flawed as it is contrasting master with master-
next which has 1.85 as well as other changes. We need to remove that
from the equation.

Cheers,

Richard