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    SubjectRe: [PATCH v2 5/6] KVM-GST: adjust scheduler cpu power
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    On Fri, 2011-01-28 at 14:52 -0500, Glauber Costa wrote:

    > +#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
    > +static DEFINE_PER_CPU(u64, cpu_steal_time);
    > +
    > +#ifndef CONFIG_64BIT
    > +static DEFINE_PER_CPU(seqcount_t, steal_time_seq);
    > +
    > +static inline void steal_time_write_begin(void)
    > +{
    > + __this_cpu_inc(steal_time_seq.sequence);
    > + smp_wmb();
    > +}
    > +
    > +static inline void steal_time_write_end(void)
    > +{
    > + smp_wmb();
    > + __this_cpu_inc(steal_time_seq.sequence);
    > +}
    > +
    > +static inline u64 steal_time_read(int cpu)
    > +{
    > + u64 steal_time;
    > + unsigned seq;
    > +
    > + do {
    > + seq = read_seqcount_begin(&per_cpu(steal_time_seq, cpu));
    > + steal_time = per_cpu(cpu_steal_time, cpu);
    > + } while (read_seqcount_retry(&per_cpu(steal_time_seq, cpu), seq));
    > +
    > + return steal_time;
    > +}
    > +#else /* CONFIG_64BIT */
    > +static inline void steal_time_write_begin(void)
    > +{
    > +}
    > +
    > +static inline void steal_time_write_end(void)
    > +{
    > +}
    > +
    > +static inline u64 steal_time_read(int cpu)
    > +{
    > + return per_cpu(cpu_steal_time, cpu);
    > +}


    > @@ -3536,6 +3592,11 @@ static int touch_steal_time(int is_idle)
    >
    > if (st) {
    > account_steal_time(st);
    > +#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
    > + steal_time_write_begin();
    > + __this_cpu_add(cpu_steal_time, steal);
    > + steal_time_write_end();
    > +#endif
    > return 1;
    > }
    > return 0;


    Why replicate all logic you've already got in patch 4? That too is
    reading steal time in a loop in kvm_account_steal_time(), why not extend
    that interface to take a cpu argument and be done with it?



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