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

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

On Mon, 2025-03-31 at 22:49 +0100, Richard Purdie via
lists.openembedded.org wrote:
> 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.

There are a direct comparison with just the patch added:

https://valkyrie.yocto.io/pub/non-release/20250331-129/testresults/buildperf-debian11/perf-debian12-vk_master-next_20250331220727_26fa862acd.html
https://valkyrie.yocto.io/pub/non-release/20250331-128/testresults/buildperf-alma8/perf-alma8-vk_master-next_20250331220715_26fa862acd.html

So the buildtime is around the same (or less with rm_work), it is hard
to say from the daya. TMPDIR is 3.6GB less and 1GB less with rm_work so
definitely improved.

Enough of an improvement in space usage I think this is worthwhile. In
general space usage does correlate with build speed.

Cheers,

Richard