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    SubjectRe: [PATCH v3 5/5] cpusets, suspend: Save and restore cpusets during suspend/resume
    On Wed, 16 May 2012, Srivatsa S. Bhat wrote:

    > What you are suggesting was precisely the v1 of this patchset, which went
    > upstream as commit 8f2f748b06562 (CPU hotplug, cpusets, suspend: Don't touch
    > cpusets during suspend/resume).
    >
    > It got reverted due to a nasty suspend hang in some corner case, where the
    > sched domains not being up-to-date got the scheduler confused.
    > Here is the thread with that discussion:
    > http://thread.gmane.org/gmane.linux.kernel/1262802/focus=1286289
    >
    > As Peter suggested, I'll try to fix the issues at the 2 places that I found
    > where the scheduler gets confused despite the cpu_active mask being up-to-date.
    >
    > But, I really want to avoid that scheduler fix and this cpuset fix from
    > being tied together, for the fear that until we root-cause and fix all
    > scheduler bugs related to cpu_active mask, we can never get cpusets fixed
    > once and for all for suspend/resume. So, this patchset does an explicit
    > save and restore to be sure, and so that we don't depend on some other/unknown
    > factors to make this work reliably.
    >

    Ok, so it seems like this is papering over an existing cpusets issue or an
    interaction with the scheduler that is buggy. There's no reason why a
    cpuset.cpus that is a superset of cpu_active_mask should cause an issue
    since that's exactly what the root cpuset has. I know root is special
    cased all over the cpuset code, but I think the real fix here is to figure
    out why it can't be left as a superset and then we end up doing nothing
    for s/r.

    I don't have a preference for cpu hotplug and whether cpuset.cpus = 1-3
    remains 1-3 when cpu 2 is offlined or not, I think it could be argued both
    ways, but I disagree with saving the cpumask, removing all suspended cpus,
    and then reinstating it for no reason.


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