lkml.org 
[lkml]   [2012]   [Aug]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/5] workqueue: change value of lcpu in queue_delayed_work_on()
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


\
 
 \ /
  Last update: 2012-08-13 23:22    [W:0.098 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site