On Fri, Jun 17, 2022 at 12:14 AM Frank Ch. Eigler <fche@xxxxxxxxxx> wrote: > > > > https://fedoraproject.org/wiki/Changes/fno-omit-frame-pointer > > [...] > > === Unwinding === > > [...] > > * Kernel 4.8 frame pointer benchmarks by Suse showed 5%-10% > > regressions in some benchmarks > > (https://lore.kernel.org/all/20170602104048.jkkzssljsompjdwy@xxxxxxx/T/#u) > > Regressions of such magnitude can veto such changes, especially when > they hit everyone, not just those who are highly dependent on the > profiling tools the proposal is concerned about. The 4.8 kernel is comparatively ancient now and a lot had changed in this area of the kernel, I think we need benchmarks on a more modern kernel with gcc12 to see if any of this has since been mitigated before we rule out the change in it's entirety. > > === Alternatives to frame pointers === > > > > There are a few alternative ways to unwind stacks instead of using the > > frame pointer: > > > * [https://dwarfstd.org DWARF] data - The compiler can emit extra > > [...] The problem is that we need to unwind the stack in kernel space > > (Are you referring to a novel kernel-resident tool?) > > > > To summarize, if we want complete stacks with reasonably low overhead > > (which we do, there's no other way to get accurate profiling data from > > running services), frame pointers are currently the best option. > > The proposal doesn't characterize the "reasonably low overhead" that > this operation targets. That makes it hard to judge the tradeoffs. > > > > [...] > > Fedora users will be more likely to have a streamlined experience when > > trying to debug/profile system executables/libraries. Tools such as > > perf will work out of the box instead of requiring to users to provide > > extra options (e.g. --call-graph=dwarf/LBR) [...] > > If typing that option were a hardship, it could be made default on > Fedora. With broad debuginfod auto-downloading capability, maybe it's > worth considering. > > > - FChE > _______________________________________________ > 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 on the list, report it: https://pagure.io/fedora-infrastructure _______________________________________________ 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 on the list, report it: https://pagure.io/fedora-infrastructure
