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    SubjectRe: [ANNOUNCE] 3.8-rc6-nohz4
    From
    2013/2/7 Ingo Molnar <mingo@kernel.org>:
    >
    > * Steven Rostedt <rostedt@goodmis.org> wrote:
    >
    >> I'll reply to this as I come up with comments.
    >>
    >> First thing is, don't call it NO_HZ_FULL. A better name would
    >> be NO_HZ_CPU. I would like to reserve NO_HZ_FULL when we
    >> totally remove jiffies :-)
    >
    > I don't think we want yet another config option named in a
    > weird way.
    >
    > What we want instead is to just split NO_HZ up into its
    > conceptual parts:
    >
    > CONFIG_NO_HZ_IDLE

    Renaming CONFIG_NO_HZ to CONFIG_NO_HZ_IDLE is something I considered.
    I was just worried about this option being present in many defconfig.
    Perhaps we can do that renaming and keep CONFIG_NO_HZ around a little
    while for backward compatibility (pretty much like what we've done for
    CONFIG_PERF_COUNTERS -> CONFIG_PERF_EVENTS).

    > CONFIG_NO_HZ_USER_SPACE
    > CONFIG_NO_HZ_KERNEL_SPACE
    >
    > Where the current status quo is NO_HZ_IDLE=y, and Frederic is
    > about to introduce NO_HZ_USER_SPACE=y. When jiffies get removed
    > we get NO_HZ_KERNEL_SPACE=y.

    Note on my tree I stop the tick on both rings. I believe that
    restarting the tick on kernel entry isn't something we should
    seriously consider. It would be a costly operation that may make
    things worse. And in fact there is no big difference. Just kernelspace
    has more opportunities to be disturbed (RCU IPIs, async timer/work
    scheduled by the kernel, etc...) and get its tick restarted sometimes.

    >
    > The 'CONFIG_NO_HZ' meta-option, which we should leave for easy
    > configurability and for compatibility, should get us the
    > currently recommended default, which for the time being might
    > be:

    Ah looks like you considered the compatibility as well :)

    >
    > CONFIG_NO_HZ_IDLE=y
    > # CONFIG_NO_HZ_USER_SPACE is disabled
    >
    > Btw., you could add CONFIG_NO_HZ_KERNEL_SPACE right away, just
    > keep it false all the time. That would document our future plans
    > pretty well.
    >
    > Once CONFIG_NO_HZ_USER_SPACE is proven problem-free, we might
    > default to:
    >
    > CONFIG_NO_HZ_IDLE=y
    > CONFIG_NO_HZ_USER_SPACE=y
    >
    > The goal is to have this in the distant future:
    >
    > CONFIG_NO_HZ=y
    >
    > CONFIG_NO_HZ_IDLE=y
    > CONFIG_NO_HZ_USER_SPACE=y
    > CONFIG_NO_HZ_KERNEL_SPACE=y
    >
    > And eventually we might even be able to get rid of all the 3
    > variants, and only offer full-on/off.
    >
    > Agreed?

    At least for now we seem to agree on CONFIG_NO_HZ_IDLE and keep
    CONFIG_NO_HZ for compatibility. Are you ok with that? If so I'll send
    a patch.


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