Hello,
On Tue, Aug 14, 2012 at 01:54:22AM +0900, JoonSoo Kim wrote:
> wq = WQ_NON_REENTRANT.
> queue_delayed_work_on(CPU B) is invoked in CPU A, so lcpu = CPU A, cpu = CPU
> B.
>
> In this case, we call add_time_on(CPU B), then delayed_work_timer_fn()
> is invoked on CPU B.
> delayed_work_timer_fn() calls __queue_work(), then following
> comparisons return true!
>
> gcwq = get_gcwq(cpu);
> if (wq->flags & WQ_NON_REENTRANT &&
> (last_gcwq = get_work_gcwq(work)) && last_gcwq != gcwq) {
>
> I thinks that if we assign cpu to lcpu, above comparisons return
> false, so save some overheads.
> Is there any missing part?
Nope, that sound correct to me.
> And, do u mean @cpu is WORK_CPU_UNBOUND?
@cpu could be WORK_CPU_UNBOUND at that point. The timer will be added
to local CPU but @work->data would be pointing to WORK_CPU_UNBOUND,
again triggering the condition. Given that @cpu being
WORK_CPU_UNBOUND is far more common than an actual CPU number, the
patch would actually increase spurious nrt lookups. The right thing
to do is probably setting cpu to raw_smp_processor_id() beforehand.
Thanks.
--
tejun
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