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    SubjectRe: [PATCH v4 12/13] fair.c: Use generic rbtree impl in fair scheduler
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    On Fri, 2012-06-22 at 23:00 -0500, Daniel Santos wrote:
    > +static inline long compare_vruntime(u64 *a, u64 *b)
    > +{
    > +#if __BITS_PER_LONG >= 64
    > + return (long)((s64)*a - (s64)*b);
    > +#else
    > +/* This is hacky, but is done to reduce instructions -- we wont use this for
    > + * rbtree lookups, only inserts, and since our relationship is defined as
    > + * non-unique, we only need to return positive if a > b and any other value
    > + * means less than.
    > + */
    > + return (long)(*a > *b);
    > +#endif
    > +}

    That's wrong.. suppose: a = 10, b = ULLONG_MAX - 10

    In that case (s64)(a - b) = 20, however a > b is false.

    And yes, vruntime wrap does happen.


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