On Tue, Oct 01, 2013 at 04:05:27PM +0200, Frederic Weisbecker wrote:
> struct cpu_idletime {
> nr_iowait,
> seqlock,
> idle_start,
> idle_time,
> iowait_time,
> } __cacheline_aligned_in_smp;
>
> DEFINE_PER_CPU(struct cpu_idletime, cpu_idletime);
>
> io_schedule()
> {
> int prev_cpu;
>
> preempt_disable();
> prev_cpu_idletime = __this_cpu_ptr(&cpu_idletime);
> atomic_inc(prev_cpu_idletime->nr_iowait);
> WARN_ON_ONCE(is_idle_task(current));
> preempt_enable_no_resched();
>
> schedule();
>
> write_seqlock(prev_cpu_idletime->seqlock)
> if (!atomic_dec_return(prev_cpu_idletime->nr_iowait))
> flush_cpu_idle_time(prev_cpu_idletime, 1)
> write_sequnlock(prev_cpu_idletime->seqlock)
>
> }
This is at least 3 atomic ops and a whole bunch of branches extra. It
used to be 2 atomics and no branches.
What again are we solving any why?
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