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Date: Thu, 26 Mar 2015 14:19:35 +0000 From: Dietmar Eggemann <dietmar.eggemann@....com> To: Vincent Guittot <vincent.guittot@...aro.org>, "peterz@...radead.org" <peterz@...radead.org>, "mingo@...nel.org" <mingo@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>, Morten Rasmussen <Morten.Rasmussen@....com>, "kamalesh@...ux.vnet.ibm.com" <kamalesh@...ux.vnet.ibm.com> CC: "riel@...hat.com" <riel@...hat.com>, "efault@....de" <efault@....de>, "nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>, "linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org> Subject: Re: [PATCH v10 11/11] sched: move cfs task on a CPU with higher capacity On 27/02/15 15:54, Vincent Guittot wrote: > When a CPU is used to handle a lot of IRQs or some RT tasks, the remaining > capacity for CFS tasks can be significantly reduced. Once we detect such > situation by comparing cpu_capacity_orig and cpu_capacity, we trig an idle > load balance to check if it's worth moving its tasks on an idle CPU. > It's worth trying to move the task before the CPU is fully utilized to > minimize the preemption by irq or RT tasks. > > Once the idle load_balance has selected the busiest CPU, it will look for an > active load balance for only two cases : > - there is only 1 task on the busiest CPU. > - we haven't been able to move a task of the busiest rq. > > A CPU with a reduced capacity is included in the 1st case, and it's worth to > actively migrate its task if the idle CPU has got more available capacity for > CFS tasks. This test has been added in need_active_balance. > > As a sidenote, this will not generate more spurious ilb because we already > trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that > has a task, we will trig the ilb once for migrating the task. > > The nohz_kick_needed function has been cleaned up a bit while adding the new > test > > env.src_cpu and env.src_rq must be set unconditionnally because they are used > in need_active_balance which is called even if busiest->nr_running equals 1 > > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org> > --- > kernel/sched/fair.c | 69 ++++++++++++++++++++++++++++++++++++----------------- > 1 file changed, 47 insertions(+), 22 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 7420d21..e70c315 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6855,6 +6855,19 @@ static int need_active_balance(struct lb_env *env) > return 1; > } > > + /* > + * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task. > + * It's worth migrating the task if the src_cpu's capacity is reduced > + * because of other sched_class or IRQs if more capacity stays > + * available on dst_cpu. > + */ > + if ((env->idle != CPU_NOT_IDLE) && > + (env->src_rq->cfs.h_nr_running == 1)) { > + if ((check_cpu_capacity(env->src_rq, sd)) && > + (capacity_of(env->src_cpu)*sd->imbalance_pct < capacity_of(env->dst_cpu)*100)) > + return 1; > + } > + > return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2); > } > > @@ -6954,6 +6967,9 @@ static int load_balance(int this_cpu, struct rq *this_rq, > > schedstat_add(sd, lb_imbalance[idle], env.imbalance); > > + env.src_cpu = busiest->cpu; Isn't this 'env.src_cpu = busiest->cpu;' or 'env.src_cpu = cpu_of(busiest);' already needed due to the existing ASYM_PACKING check in need_active_balance() 'if ( ... && env->src_cpu > env->dst_cpu)' for CPU_NEWLY_IDLE? Otherwise like you said, in these 'busiest->nr_running equals 1' instances, env->src_cpu is un-initialized. > + env.src_rq = busiest; > + > ld_moved = 0; > if (busiest->nr_running > 1) { > /* > @@ -6963,8 +6979,6 @@ static int load_balance(int this_cpu, struct rq *this_rq, > * correctly treated as an imbalance. > */ > env.flags |= LBF_ALL_PINNED; > - env.src_cpu = busiest->cpu; > - env.src_rq = busiest; > env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running); > > more_balance: [...] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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