Re: [PATCH 01/13] objtool: Rewrite hashtable sizing

[Peter Zijlstra]

On Thu, Jun 10, 2021 at 11:14:51AM -0700, Nathan Chancellor wrote:

> This patch as commit 25cf0d8aa2a3 ("objtool: Rewrite hashtable sizing")
> in -tip causes a massive compile time regression with allmodconfig +
> ThinLTO.

Moo... the allyesconfig builds I used it on were much faster, but that
was on regular GCC vmlinux.o after linking.

> Adding Sami because I am not sure why this patch would have much of an impact
> in relation to LTO. https://git.kernel.org/tip/25cf0d8aa2a3 is the patch in
> question.
> 
> If I can provide any further information or help debug, please let me know.
> 
> If you are interested in reproducing this locally, you will need a
> fairly recent LLVM stack (I used the stable release/12.x branch) and to
> cherry-pick commit 976aac5f8829 ("kcsan: Fix debugfs initcall return
> type") to fix an unrelated build failure. My script [2] can build a
> self-contained toolchain fairly quickly if you cannot get one from your
> package manager. A command like below will speed up the build a bit:

Would something like llvm-13 from Debian be good enough?

$ clang-13 --version
Debian clang version 13.0.0-++20210418105309+a0898f0cecc7-1~exp1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin