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    SubjectRe: [PATCH v4 0/7] x86: BSP or CPU0 online/offline
    On 12/06/2011 02:12 PM, Ingo Molnar wrote:

    >
    > * Fenghua Yu <fenghua.yu@intel.com> wrote:
    >
    >> From: Fenghua Yu <fenghua.yu@intel.com>
    >>
    >> BSP or CPU0 has been the last obstacle to CPU hotplug on x86.
    >> This patch set implements BSP online and offline and removes
    >> this obstacle to CPU hotplug.

    [snip]
    >

    > Also, could you please enumerate all limitations that could
    > possibly happen? The documentation has this list right now:
    >
    > +1. Resume from hibernate/suspend depends on BSP. Hibernate/suspend will fail if
    > +BSP is offline and you need to online BSP before hibernate/suspend can continue.
    >
    > This needs to be fixed on some other fashion than warning people
    > in documentation that it would break.
    >


    Actually, this patchset does more than just warn people. It has
    checks to see if the CPU0 is offline, and if so, it fails the
    suspend/hibernate attempt. See patch 7/7
    (x86/power/cpu.c: Don't hibernate/suspend if CPU0 is offline)

    > Firstly, at minimum a suspend/hibernate attempt should fail in
    > some deterministic fashion.


    It does, as mentioned above. In fact, this patchset does it
    proactively: whether the hardware/firmware supports suspend/resume
    with BSP offlined or not, it just prevents anybody from doing
    suspend/hibernate when the boot CPU is offline.

    I am not saying that this is the *right* way to do it; I am just
    pointing out that this patchset _does_ handle it.

    >
    > Secondly, and more importantly, is there *any* hardware in
    > existence that has a BIOS that can suspend/resume successfully
    > with BSP offlined? If such hardware exists then we need to
    > support it properly - initially perhaps by whitelisting such
    > systems.
    >
    > Then if demand for this picks up some more intelligent method of
    > cooperating with the firmware could be added: the firmware could
    > actually signal to us whether it supports suspend/resume from
    > other than the boot CPU.
    >


    Regards,
    Srivatsa S. Bhat



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