We've known for a while that the current policy of shipping Rawhide kernels with debug enabled leads to a pretty big performance hit for a large number of people. A while ago Justin, Adam Williamson, Kevin Fenzi, and I (with the help of others) dug in and figured out that most of this impact comes from having SLUB debugging turned on and enabled by default. We took two measures to help alleviate some of this. The first was that we ship the first -rcX build, and each final kernel release build, with debug disabled. The second was that Justin got the Rawhide NoDebug repo up and running. Both of those steps seemed to help, and the NoDebug repo has been a success as far as we can tell. Which is to say that people tell us they use it, and they complain when it isn't up to date. However, even the most ardent Rawhide testers seem to have realized that booting with slub_debug=- gets them what they need and made it their default way of running kernels. Basically, that negates the value of having it enabled for the majority of the people actually bothering to run Rawhide kernels in the first place. After discussing it with the rest of the team and realizing that the runtime enable/disable function works both ways, we're going to start disabling SLUB debug by default in Rawhide kernels starting with 3.14 for all kernel builds after the corresponding -rc1 release. I spent some time looking through bugzilla and realized that most of the SLUB debugging stuff that gets caught happens in the merge window kernels (pre-rc1), so we'll leave it enabled for the merge window to catch the stuff happening there. After -rc1 is released, it will remain disabled by default. So to summarize: - SLUB debugging will only be enabled by default on merge window snapshot kernels - No other debug options are changing, as we're doing this to address a specific problem. This is not a flag day, and things like lockdep debugging and other options are still very helpful. That means for those wanting all debug options disabled, the NoDebug repo is where you want to go. Hopefully this makes Rawhide a bit more usable for people, which will correlate with an uptick in it being used. If you have any questions, let us know. As an aside, Dave brought up that it might be nice to have a script that we could run to sort of "debugize" a non-debug kernel. Things like switching on slub debugging, disabling 'rhgb' and 'quiet' from the default command line, or any other runtime tunables that we can think of. Rather than asking for things piecemeal, we could just have the user run such a script to help them get us debugging information. If someone is interested in scripting something like that, please speak up! josh _______________________________________________ kernel mailing list kernel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/kernel
