Messages in this thread | | | Date | Tue, 14 Aug 2012 01:54:22 +0900 | Subject | Re: [PATCH 2/5] workqueue: change value of lcpu in queue_delayed_work_on() | From | JoonSoo Kim <> |
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2012/8/14 Tejun Heo <tj@kernel.org>: > Hello, > > On Tue, Aug 14, 2012 at 01:17:49AM +0900, Joonsoo Kim wrote: >> We assign cpu id into work struct in queue_delayed_work_on(). >> In current implementation, when work is come in first time, >> current running cpu id is assigned. >> If we do queue_delayed_work_on() with CPU A on CPU B, >> __queue_work() invoked in delayed_work_timer_fn() go into sub-optimal path >> in case of WQ_NON_REENTRANT. >> Change it to cpu argument is prevent to go into sub-optimal path. > > Which part is suboptimal? Also, what if @cpu is WQ_UNBOUND?
Hi. I think a following scenario.
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?
And, do u mean @cpu is WORK_CPU_UNBOUND?
Thanks.
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