| Message ID | 1436293469-25707-37-git-send-email-morten.rasmussen@arm.com (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
On Tue, Jul 07, 2015 at 07:24:19PM +0100, Morten Rasmussen wrote: > Scenarios with the busiest group having just one task and the local > being idle on topologies with sched groups with different numbers of > cpus manage to dodge all load-balance bailout conditions resulting the > nr_balance_failed counter to be incremented. This eventually causes an > pointless active migration of the task. This patch prevents this by not > incrementing the counter when the busiest group only has one task. > ASYM_PACKING migrations and migrations due to reduced capacity should > still take place as these are explicitly captured by > need_active_balance(). > > A better solution would be to not attempt the load-balance in the first > place, but that requires significant changes to the order of bailout > conditions and statistics gathering. *groan*, and this is of course triggered by your 2+3 core TC2 thingy. Yes, asymmetric groups like that are a pain. -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8e0cbd4..f7cb6c9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6127,6 +6127,7 @@ struct lb_env { int new_dst_cpu; enum cpu_idle_type idle; long imbalance; + unsigned int src_grp_nr_running; /* The set of CPUs under consideration for load-balancing */ struct cpumask *cpus; @@ -7150,6 +7151,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd if (env->sd->flags & SD_NUMA) env->fbq_type = fbq_classify_group(&sds->busiest_stat); + env->src_grp_nr_running = sds->busiest_stat.sum_nr_running; + if (!env->sd->parent) { /* update overload indicator if we are at root domain */ if (env->dst_rq->rd->overload != overload) @@ -7788,7 +7791,8 @@ static int load_balance(int this_cpu, struct rq *this_rq, * excessive cache_hot migrations and active balances. */ if (idle != CPU_NEWLY_IDLE) - sd->nr_balance_failed++; + if (env.src_grp_nr_running > 1) + sd->nr_balance_failed++; if (need_active_balance(&env)) { raw_spin_lock_irqsave(&busiest->lock, flags);
Scenarios with the busiest group having just one task and the local being idle on topologies with sched groups with different numbers of cpus manage to dodge all load-balance bailout conditions resulting the nr_balance_failed counter to be incremented. This eventually causes an pointless active migration of the task. This patch prevents this by not incrementing the counter when the busiest group only has one task. ASYM_PACKING migrations and migrations due to reduced capacity should still take place as these are explicitly captured by need_active_balance(). A better solution would be to not attempt the load-balance in the first place, but that requires significant changes to the order of bailout conditions and statistics gathering. cc: Ingo Molnar <mingo@redhat.com> cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> --- kernel/sched/fair.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)