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    SubjectRe: [PATCH RFC 0/8] jump-label: allow early jump_label_enable()
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    On Thu, 2011-09-29 at 21:40 -0700, Jeremy Fitzhardinge wrote:
    > On 09/29/2011 05:52 PM, Steven Rostedt wrote:
    > > On Thu, 2011-09-29 at 16:26 -0700, Jeremy Fitzhardinge wrote:
    > >> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    > >>
    > >> One big question which arises is whether the _early() function is
    > >> necessary at all. All the stop_machine/mutex/etc stuff that
    > >> arch_jump_label_transform() ends up doing is redundant pre-SMP, but it
    > >> shouldn't hurt. Maybe we can just drop the _early function? It works
    > >> on x86, at least, because jump_label_enable() works, which uses the full
    > >> form. And dropping it would reduce this to a very much smaller series.
    > > It does slow down the boot process, which is not a good thing when
    > > everyone is pushing for the fastest restarts.
    >
    > Would it really though? stop_machine() doesn't do very much when there
    > are no other cpus.
    >
    > Not that I measured or anything, but there was no obvious big lag at boot.

    Just bringing up the point, but without measurements, its all hand
    waving. It may not be a big deal, and simpler code is always better if
    it doesn't harm anything else.

    >
    > > What we should probably do is have a global read_mostly variable called,
    > > smp_activated or something, then things that can be called before and
    > > after can read this variable to determine if it can skip certain
    > > protections.
    >
    > Could do that if it turns out to be a problem.
    >
    > > While we're at it, perhaps we could add a memory_initialized for things
    > > like tracers that want to trace early but need to wait till it can
    > > allocate buffers. If we had this flag, it could instead do an early
    > > memory init to create the buffers.
    >
    > That seems orthogonal to the jump_label changes.

    It is. But it's something that bugs me and this just reminded me of
    it ;)

    -- Steve




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