Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 11 Sep 2014 14:14:52 +0200 | Subject | Re: [PATCH v5 08/12] sched: move cfs task on a CPU with higher capacity |
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On 11 September 2014 12:13, Peter Zijlstra <peterz@infradead.org> wrote: > On Tue, Aug 26, 2014 at 01:06:51PM +0200, Vincent Guittot wrote: > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 18db43e..60ae1ce 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6049,6 +6049,14 @@ static bool update_sd_pick_busiest(struct lb_env *env, >> return true; >> } >> >> + /* >> + * The group capacity is reduced probably because of activity from other >> + * sched class or interrupts which use part of the available capacity >> + */ >> + if ((sg->sgc->capacity_orig * 100) > (sgs->group_capacity * >> + env->sd->imbalance_pct)) >> + return true; >> + >> return false; >> } >> >> @@ -6534,13 +6542,23 @@ static int need_active_balance(struct lb_env *env) >> struct sched_domain *sd = env->sd; >> >> if (env->idle == CPU_NEWLY_IDLE) { >> + int src_cpu = env->src_cpu; >> >> /* >> * ASYM_PACKING needs to force migrate tasks from busy but >> * higher numbered CPUs in order to pack all tasks in the >> * lowest numbered CPUs. >> */ >> - if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu) >> + if ((sd->flags & SD_ASYM_PACKING) && src_cpu > env->dst_cpu) >> + return 1; >> + >> + /* >> + * If the CPUs share their cache and the src_cpu's capacity is >> + * reduced because of other sched_class or IRQs, we trig an >> + * active balance to move the task >> + */ >> + if ((capacity_orig_of(src_cpu) * 100) > (capacity_of(src_cpu) * >> + sd->imbalance_pct)) >> return 1; >> } > > Should you not also check -- in both cases -- that the destination is > any better?
The case should have been solved earlier when calculating the imbalance which should be null if the destination is worse than the source.
But i haven't formally check that calculate_imbalance correctly handles that case
> > Also, there's some obvious repetition going on there, maybe add a > helper?
yes
> > Also, both sites should probably ensure they're operating in the > non-saturated/overloaded scenario. Because as soon as we're completely > saturated we want SMP nice etc. and that all already works right > (presumably).
If both are overloaded, calculated_imbalance will cap the max load that can be pulled so the busiest_group will not become idle
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