* Ben Cotton: > * Meta builds all its libraries and executables with > -fno-omit-frame-pointer by default. Internal benchmarks did not show > significant impact on performance when omitting the frame pointer for > two of our most performance intensive applications. They probably saw *significant* (in the statistics sense) performance regressions, but deemed them acceptable. > * Firefox recently landed a change to preserve the frame pointer in > all jitted code > (https://bugzilla.mozilla.org/show_bug.cgi?id=1426134). No significant > decrease in performance was observed. That could because they have to do stack walking as part of regular operation. So I'm not sure if this an appropriate comparison. It's also possible that the JIT compiler had issues that prevented it from taking full advantage of a larger register file. What you see on the Mozilla ticket is stuff that broke with the slightly smaller register set. That is going to bite some packages on i686. (It's not going to impact x86-64, I think.) > * [https://lwn.net/Articles/680985 LBR] - New Intel CPUs have a > feature that gives you source and target addresses for the last 16 (or > 32, in newer CPUs) branches with no overhead. It can be configured to > record only function calls and to be used as a stack, which means it > can be used to get the stack trace. Sadly, you only get the last X > calls, and not the full stack trace, so the data can be very > incomplete. On top of that, many Fedora users might still be using > CPUs without LBR support which means we wouldn't be able to assume > working profilers on a Fedora system by default. Do you really need more than five or so *physical* stack frames during profiling, to figure out what is going on? Graphs generated from DWARF unwinding typically will show logical stack frames from inlining, too, and appear much deeper. Thanks, Florian _______________________________________________ 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
