Messages in this thread | | | Date | Tue, 1 Oct 2013 17:00:37 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock |
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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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