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    SubjectRe: [PATCH v2 0/7] CPU hotplug, cpusets: Fix issues with cpusets handling upon CPU hotplug
    On Fri, 2012-05-04 at 22:14 +0200, Peter Zijlstra wrote:
    > > Also, we need to fix this problem at the CPU Hotplug level itself, and
    > > not just for the suspend/resume case. Because, we have had numerous bug
    > > reports and people complaining about this issue, in various scenarios,
    > > including those that didn't involve suspend/resume.
    > NO, absolutely not and I will NAK any and all such nonsense. WTF is a
    > cpuset worth if you can run on random other cpus?

    Sorting your cpuset 'problem' isn't nowhere near enough to make hotplug
    'safe'. unplug also destroys task_struct::cpus_allowed.

    Try it:

    # schedtool -a 2 $$
    # grep Cpus_allowed /proc/self/status
    Cpus_allowed: 000004
    # echo 0 > /sys/devices/system/cpu/cpu2/online
    # grep Cpus_allowed /proc/self/status
    Cpus_allowed: ffffff

    See, hotplug is destructive, it has to be, there's no saying the cpu
    will every come back.

    So mucking about trying to make cpusets non-destructive is pointless.

    The real bug is people using hotplug (for all kinds of stupid stuff) and
    expecting anything different.

     \ /
      Last update: 2012-05-04 23:01    [W:0.023 / U:45.564 seconds]
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