On 04/02/2015 11:29 AM, Jason Low wrote: > On Wed, 2015-04-01 at 18:04 +0100, Morten Rasmussen wrote: >> On Wed, Apr 01, 2015 at 07:49:56AM +0100, Preeti U Murthy wrote: > >>> I am sorry I don't quite get this. Can you please elaborate? >> >> I think the scenario is that we are in nohz_idle_balance() and decide to >> bail out because we have pulled some tasks, but before leaving >> nohz_idle_balance() we want to check if more balancing is necessary >> using nohz_kick_needed() and potentially kick somebody to continue. > > Also, below is an example patch. > > (Without the conversion to idle_cpu(), the check for rq->idle_balance > would not be accurate anymore) > > --- > kernel/sched/fair.c | 17 ++++++++++------- > 1 files changed, 10 insertions(+), 7 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index fdae26e..7749a14 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -7620,6 +7620,8 @@ out: > } > > #ifdef CONFIG_NO_HZ_COMMON > +static inline bool nohz_kick_needed(struct rq *rq); > + > /* > * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the > * rebalancing for all the cpus for whom scheduler ticks are stopped. > @@ -7629,6 +7631,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum > cpu_idle_type idle) > int this_cpu = this_rq->cpu; > struct rq *rq; > int balance_cpu; > + bool done_balancing = false; > > if (idle != CPU_IDLE || > !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) > @@ -7644,7 +7647,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum > cpu_idle_type idle) > * balancing owner will pick it up. > */ > if (need_resched()) > - break; > + goto end; > > rq = cpu_rq(balance_cpu); > > @@ -7663,9 +7666,12 @@ static void nohz_idle_balance(struct rq *this_rq, enum > cpu_idle_type idle) > if (time_after(this_rq->next_balance, rq->next_balance)) > this_rq->next_balance = rq->next_balance; > } > + done_balancing = true; > nohz.next_balance = this_rq->next_balance; > end: > clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); > + if (!done_balancing && nohz_kick_needed(this_rq)) > + nohz_balancer_kick(); > } > > /* > @@ -7687,7 +7693,7 @@ static inline bool nohz_kick_needed(struct rq *rq) > int nr_busy, cpu = rq->cpu; > bool kick = false; > > - if (unlikely(rq->idle_balance)) > + if (unlikely(idle_cpu(cpu))) > return false; > > /* > @@ -7757,16 +7763,13 @@ static void run_rebalance_domains(struct > softirq_action *h) > enum cpu_idle_type idle = this_rq->idle_balance ? > CPU_IDLE : CPU_NOT_IDLE; > > + rebalance_domains(this_rq, idle); > /* > * If this cpu has a pending nohz_balance_kick, then do the > * balancing on behalf of the other idle cpus whose ticks are > - * stopped. Do nohz_idle_balance *before* rebalance_domains to > - * give the idle cpus a chance to load balance. Else we may > - * load balance only within the local sched_domain hierarchy > - * and abort nohz_idle_balance altogether if we pull some load. > + * stopped. > */ > nohz_idle_balance(this_rq, idle); > - rebalance_domains(this_rq, idle); > }
Ok this patch looks good. Let me test to find out if scheduling behavior improves. Regards Preeti U Murthy > > /* > -- 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/
