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    SubjectRe: CPU hotplug on i386
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    Date
    Hi.

    On Thu, 2005-03-17 at 01:40, Rafael J. Wysocki wrote:
    > On Wednesday, 16 of March 2005 14:21, Pavel Machek wrote:
    > > Hi!
    > >
    > > I tried to solve long-standing uglyness in swsusp cmp code by calling
    > > cpu hotplug... only to find out that CONFIG_CPU_HOTPLUG is not
    > > available on i386. Is there way to enable CPU_HOTPLUG on i386?
    >
    > Heh, that's exactly what I was thinking about. ;-)
    >
    > AFAICS we don't need the full CPU hotplug to do this. For suspend, we need to
    > enable the CPU hotplug-related code in sched.c and cpu.c, and we need to
    > implement the functions __cpu_disable() and __cpu_die() (called from within
    > cpu.c) on each architecture for which we want swsusp to work on SMP.
    >
    > If that's acceptable, the CPU hotplug code in sched.c and cpu.c may be
    > enabled by changing some #ifdefs there. For example, we could replace the
    >
    > #idef CONFIG_CPU_HOTPLUG
    >
    > with
    >
    > #if defined(CONFIG_CPU_HOTPLUG) || (defined(CONFIG_SOFTWARE_SUSPEND)
    > && defined(CONFIG_SMP))
    >
    > wherever necessary.
    >
    > The implementation of __cpu_disable() and __cpu_die() may be a bit more
    > tricky, however. In __cpu_disable() we need to save the settings of the local
    > APIC of each CPU (on x86-64, at least) etc. In __cpu_die() we should give the
    > "frozen" CPU some "neutral" code to execute, it seems (or "hlt" it?).
    >
    > I've looked at the ia64 implementation of these functions, but I haven't fully
    > understood it yet.

    It would be good (32 bit) if you handled MTRRs as well. Putting their
    save/restore code in the driver model is racy (SMP calls). I've worked
    around that in Suspend2 by removing the driver model support and making
    the save/restore calls from the lowlevel code. I think this should be
    considered the right thing to do.

    By the way, I'm keen to test this with Suspend2 as well. I would have
    done so before now, but I didn't realise Zwane had the support done.

    Regards,

    Nigel
    --
    Nigel Cunningham
    Software Engineer, Canberra, Australia
    http://www.cyclades.com
    Bus: +61 (2) 6291 9554; Hme: +61 (2) 6292 8028; Mob: +61 (417) 100 574

    Maintainer of Suspend2 Kernel Patches http://suspend2.net

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