On Thu, 2012-09-13 at 10:19 +0200, Peter Zijlstra wrote: > On Thu, 2012-09-13 at 08:49 +0200, Mike Galbraith wrote: > > On Thu, 2012-09-13 at 06:11 +0200, Vincent Guittot wrote: > > > On tickless system, one CPU runs load balance for all idle CPUs. > > > The cpu_load of this CPU is updated before starting the load balance > > > of each other idle CPUs. We should instead update the cpu_load of the > > > balance_cpu. > > > > > > Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> > > > --- > > > kernel/sched/fair.c | 11 ++++++----- > > > 1 file changed, 6 insertions(+), 5 deletions(-) > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > index 1ca4fe4..9ae3a5b 100644 > > > --- a/kernel/sched/fair.c > > > +++ b/kernel/sched/fair.c > > > @@ -4794,14 +4794,15 @@ static void nohz_idle_balance(int this_cpu, enum > > > cpu_idle_type idle) > > > if (need_resched()) > > > break; > > > > > > - raw_spin_lock_irq(&this_rq->lock); > > > - update_rq_clock(this_rq); > > > - update_idle_cpu_load(this_rq); > > > - raw_spin_unlock_irq(&this_rq->lock); > > > + rq = cpu_rq(balance_cpu); > > > + > > > + raw_spin_lock_irq(&rq->lock); > > > + update_rq_clock(rq); > > > + update_idle_cpu_load(rq); > > > + raw_spin_unlock_irq(&rq->lock); > > > > > > rebalance_domains(balance_cpu, CPU_IDLE); > > > > > > - rq = cpu_rq(balance_cpu); > > > if (time_after(this_rq->next_balance, rq->next_balance)) > > > this_rq->next_balance = rq->next_balance; > > > } > > > > Ew, banging locks and updating clocks to what good end? > > Well, updating the load statistics on the cpu you're going to balance > seems like a good end to me.. ;-) No point updating the local statistics > N times and leaving the ones you're going to balance stale for god knows > how long.
Sure, the goal is fine, but I wonder about the price vs payoff. I was thinking perhaps the redundant updates should go away instead, unless stats are shown to be causing real world pain. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
