Your personal non-LTO package lists

alamahant · Advocate Joined: 23 Mar 2019 Posts: 3879

Hi experienced compiler friends.

I am trying to create a list of packages that either do not compile properly or have sub optimal performance if built with LTO flags.
Would you care to share some of them with the community?

Also plz feel free to add any other relevant info if you wish ,like for example which flags do you prefer etc..........
Thanks a lot Guys...
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Goverp · Advocate Joined: 07 Mar 2007 Posts: 2008

Not sure whether it's significant, but compiling kernel 5.12.x with Clang and LTO-thin produces something about the same size as GCC non_LTO; with LTO-full, it gets bigger! That's not the experience recorded on the Internet, where people mostly seem to think the benefits are a reduction in kernel size.

You can see the LTO step in the kernel compilation listing, and sit there waiting ... With LTO-thin, on my box it was perhaps less than a minute (I didn't time it); LTO-full was several minutes.

I've no idea if there's any performance gain - if there is, it doesn't seem noticeable to the end-user. It's not damaged stability.

As an aside, all my modules seem to get LTO'd, except one that's completely external for my RTL WiFi card (still not in the kernel), which I couldn't get compiled with Clang and LTO., so it's still GCC'd. No problem using it though.
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Greybeard

alamahant · Advocate Joined: 23 Mar 2019 Posts: 3879

Goverp
Thanks for the insights

So basically if one wants to venture in LTO land it is better to use clang+lto-thin than GCC?
Also this widely broadcasted benefit of smaller binaries with LTO I havent yet seen.
Either they are the same size or slightly larger than non-LTO packages.
I used

alamahant · Advocate Joined: 23 Mar 2019 Posts: 3879

I did some research in lto-overlay and i found these

Goverp · Advocate Joined: 07 Mar 2007 Posts: 2008

mrbassie · l33t Joined: 31 May 2013 Posts: 772 Location: over here

alamahant · Advocate Joined: 23 Mar 2019 Posts: 3879

Goverp
Thanks for the link.
I noticed that both gcc flto=n and clang flto=thin produce best results in small binaries.
For example
coreutils
made with LTO has SIGNIFICANTLY smaller binaries whereas
other packages with large binaries like qemu for example is a disaster made with LTO.The lto binaries are MUCH MUCH larger.Not consistently but there seems to be a pattern.
So i feel LTO should be used in a limited way and not universally.

I really like your link about kernel building.
The way i like to make my kernels is to emerge
gentoo-sources
throw in an Arch .config and run make etc.
Do you think I can use your script in this way.
I think kernels are good candidates for LTO since they have many many small binaries......
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Perfect Gentleman · Veteran Joined: 18 May 2014 Posts: 1249

I can tell for sure that generally Clang+ThinLTO produces smaller binaries that GCC+LTO.

shoober420 · Apprentice Joined: 22 May 2017 Posts: 223

Adding upon mrbassie‘s list, these are a list of packages i’ve personally needed to disable LTO, or adjust other flags for.

https://github.com/shoober420/rootscripts/blob/main/etc/portage/package.env

https://github.com/shoober420/rootscripts/tree/main/etc/portage/env

Just as mrbassie doesn’t use the LTOoverlay, this method does not require the LTOoverlay either, which I disabled.