Re: enabling link time optimizations in package builds
On Fri, Jun 17, 2022 at 10:18:43AM +0200, Matthias Klose wrote:
>...
> The proposal is to turn on LTO by default on most 64bit release
> architectures.
>...
By what factor does -ffat-lto-objects increase disk space usage during
package builds?
Please coordinate with DSA to ensure that the buildds on these
architectures have sufficient diskspace.
amd64 buildds have/had(?) only 74 GB of diskspace, which has even
without LTO already forced some packages to do manual cleanup steps
during the build to stay within the limited disk space.
>...
> Link time
> optimizations are also at least turned on in other distros like Fedora,
> OpenSuse (two years) and Ubuntu (one year).
>...
> The idea is to file wishlist bug reports for those 373 packages and then see
> how far we get, and if it's feasible to already turn on LTO for bookworm.
> If not, it should be turned on by default for the following release.
I assume these 373 packages have already been fixed/workarounded in Ubuntu?
Submitting 373 bugs with patches should settle the feasibility question.
A bigger worry is the schedule of such a change.
A major toolchain change shortly before the freeze means the vast
majority of packages will be shipped with non-LTO builds in the release,
with security updates or point release updates triggering a change to
an LTO built package.
This means few packages actually benefitting from LTO, but a higher
regression risk when fixing bugs in stable.
The best timing for such a change would be immediately after the release
of bookworm.
> Matthias
cu
Adrian
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