Hi Linus! On Tue, 2023-09-19 at 10:25 -0700, Linus Torvalds wrote: > On Tue, 19 Sept 2023 at 06:48, John Paul Adrian Glaubitz > <glaubitz@xxxxxxxxxxxxxxxxxxx> wrote: > > > > As Geert poined out, I'm not seeing anything particular problematic with the > > architectures lacking CONFIG_PREEMPT at the moment. This seems to be more > > something about organizing KConfig files. > > It can definitely be problematic. > > Not the Kconfig file part, and not the preempt count part itself. > > But the fact that it has never been used and tested means that there > might be tons of "this architecture code knows it's not preemptible, > because this architecture doesn't support preemption". > > So you may have basic architecture code that simply doesn't have the > "preempt_disable()/enable()" pairs that it needs. > > PeterZ mentioned the generic entry code, which does this for the entry > path. But it actually goes much deeper: just do a > > git grep preempt_disable arch/x86/kernel > > and then do the same for some other architectures. > > Looking at alpha, for example, there *are* hits for it, so at least > some of the code there clearly *tries* to do it. But does it cover all > the required parts? If it's never been tested, I'd be surprised if > it's all just ready to go. Thanks for the detailed explanation. > I do think we'd need to basically continue to support ARCH_NO_PREEMPT > - and such architectures migth end up with the worst-cast latencies of > only scheduling at return to user space. Great to hear, thank you. And, yes, eventually I would be happy to help get alpha and m68k converted. Adrian -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer `. `' Physicist `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
