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    SubjectRe: [linux-pm] [PATCH 0/8] Suspend block api (version 8)
    From
    2010/6/2 mark gross <640e9920@gmail.com>:
    > On Tue, Jun 01, 2010 at 08:50:02PM -0700, Arve Hjønnevåg wrote:
    >> On Tue, Jun 1, 2010 at 7:05 AM, mark gross <640e9920@gmail.com> wrote:
    >> > On Tue, Jun 01, 2010 at 09:07:37AM +0200, Florian Mickler wrote:
    >> ...
    >> >> +static void update_target_val(int pm_qos_class, s32 val)
    >> >> +{
    >> >> +     s32 extreme_value;
    >> >> +     s32 new_value;
    >> >> +     extreme_value = atomic_read(&pm_qos_array[pm_qos_class]->target_value);
    >> >> +     new_value = pm_qos_array[pm_qos_class]->comparitor(val,extreme_value);
    >> >> +     if (extreme_value != new_value)
    >> >> +             atomic_set(&pm_qos_array[pm_qos_class]->target_value,new_value);
    >> >> +}
    >> >> +
    >> >
    >> > Only works 1/2 the time, but I like the idea!
    >> > It fails to get the righ answer when constraints are reduced.  But, this
    >> > idea is a good improvement i'll roll into the next pm_qos update!
    >> >
    >>
    >> I think it would be a better idea to track your constraints with a
    >> sorted data structure. That way you can to better than O(n) for both
    >> directions. If you have a lot of constraints with the same value, it
    >> may even be worthwhile to have a two stage structure where for
    >> instance you use a rbtree for the unique values and list for identical
    >> constraints.
    >
    > I don't agree, we went through this tree vrs list discussion a few times
    > before in other areas of the kernel.  Wherever the list tended to be
    > short, a simple list wins.  However; we can try it, after we have some
    > metrics and stress test cases identified we can measure its effectivenes
    > against.
    >

    The list is not short. You have all the inactive and active
    constraints on the same list. If you change it to a two level list
    though, the list of unique values (which is the list you have to walk)
    may be short enough for a tree to be overkill.

    --
    Arve Hjønnevåg
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