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. Jakub -- _______________________________________________ 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
