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    SubjectRe: CONFIG_ISOLATION=y (was: [PATCH 0/6] support "dataplane" mode for nohz_full)

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > On Tue, May 12, 2015 at 11:10:32AM +0200, Ingo Molnar wrote:
    > >
    > > So I'd vote for Frederic's CONFIG_ISOLATION=y, mostly because this
    > > is a high level kernel feature, so it won't conflict with
    > > isolation concepts in lower level subsystems such as IOMMU
    > > isolation - and other higher level features like scheduler
    > > isolation are basically another partial implementation we want to
    > > merge with all this...
    >
    > But why do we need a CONFIG flag for something that has no content?
    >
    > That is, I do not see anything much; except the 'I want to stay in
    > userspace and kill me otherwise' flag, and I'm not sure that
    > warrants a CONFIG flag like this.
    >
    > Other than that, its all a combination of NOHZ_FULL and
    > cpusets/isolcpus and whatnot.

    Yes, that's what I meant: CONFIG_ISOLATION would trigger what is
    NO_HZ_FULL today - we could possibly even remove CONFIG_NO_HZ_FULL as
    an individual Kconfig option?

    CONFIG_ISOLATION=y would express the guarantee from the kernel that
    it's possible for user-space to configure itself to run undisturbed -
    instead of the current inconsistent set of options and facilities.

    A bit like CONFIG_PREEMPT_RT is more than just preemptable spinlocks,
    it also tries to offer various facilities and tune the defaults to
    turn the kernel hard-rt.

    Does that make sense to you?

    Thanks,

    Ingo



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