On Thu, 31 Oct 2024 at 07:32, Jakub Jelinek <jakub@xxxxxxxxxx> wrote: > > On Wed, Oct 30, 2024 at 10:46:01PM -0400, Neal Gompa wrote: > > I know the idea of moving to -O3 has been briefly mentioned before in > > other contexts when we've discussed uplifting the flags, but it looks > > like Ubuntu is moving to -O3 for Ubuntu 25.04[1]. Is there a reason > > why we shouldn't consider doing the same for Fedora Linux 42? > > Yes, this is a very bad idea. > > -O3 significantly increases code size (and the speed up gains aren't really > guaranteed), which is highly undesirable when the vast majority of code in > the distro isn't performance critical, the I-cache footprint is then more > important. Especially when -O2 in GCC performs some vectorization already > for years and it is going to be used more at -O2 in GCC 15 (but the > heuristics for -O2 vectorization is avoid significant code increases). > > -O3 should be used just for performance critical code, which is found to be > hot in profiling and proved to help performance of the code. > Better yet, performance criticial code should use PGO (profile guided > optimizations) so that only the hot parts of the code are automatically > optimized for speed and cold parts for size. With reasonable workload used > during package build for the profile feedback generation. > > There are some packages in the distro which use PGO (e.g. gcc itself), but > I think e.g. SUSE packages use PGO far more often than in Fedora. How does SUSE choose to use PGO? Is that a manual process where the maintainer chooses to turn it on for a particular library or binary? -- _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
