From 04f733b4afac5dc93ae9b0a8703c60b87def491e Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 11 May 2012 00:12:02 +0200 Subject: sched/fair: Revert sched-domain iteration breakage Patches c22402a2f ("sched/fair: Let minimally loaded cpu balance the group") and 0ce90475 ("sched/fair: Add some serialization to the sched_domain load-balance walk") are horribly broken so revert them. The problem is that while it sounds good to have the minimally loaded cpu do the pulling of more load, the way we walk the domains there is absolutely no guarantee this cpu will actually get to the domain. In fact its very likely it wont. Therefore the higher up the tree we get, the less likely it is we'll balance at all. The first of mask always walks up, while sucky in that it accumulates load on the first cpu and needs extra passes to spread it out at least guarantees a cpu gets up that far and load-balancing happens at all. Since its now always the first and idle cpus should always be able to balance so they get a task as fast as possible we can also do away with the added serialization. Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-rpuhs5s56aiv1aw7khv9zkw6@git.kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 2 -- kernel/sched/fair.c | 19 +++++++------------ 2 files changed, 7 insertions(+), 14 deletions(-) (limited to 'kernel/sched') diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0738036fa569..24922b7ff567 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5976,7 +5976,6 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu) sg->sgp = *per_cpu_ptr(sdd->sgp, cpumask_first(sg_span)); atomic_inc(&sg->sgp->ref); - sg->balance_cpu = -1; if (cpumask_test_cpu(cpu, sg_span)) groups = sg; @@ -6052,7 +6051,6 @@ build_sched_groups(struct sched_domain *sd, int cpu) cpumask_clear(sched_group_cpus(sg)); sg->sgp->power = 0; - sg->balance_cpu = -1; for_each_cpu(j, span) { if (get_group(j, sdd, NULL) != group) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9bd3366dbb1c..a259a614b394 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3776,8 +3776,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, int *balance, struct sg_lb_stats *sgs) { unsigned long load, max_cpu_load, min_cpu_load, max_nr_running; - unsigned int balance_cpu = -1; - unsigned long balance_load = ~0UL; + unsigned int balance_cpu = -1, first_idle_cpu = 0; unsigned long avg_load_per_task = 0; int i; @@ -3794,11 +3793,12 @@ static inline void update_sg_lb_stats(struct lb_env *env, /* Bias balancing toward cpus of our domain */ if (local_group) { - load = target_load(i, load_idx); - if (load < balance_load || idle_cpu(i)) { - balance_load = load; + if (idle_cpu(i) && !first_idle_cpu) { + first_idle_cpu = 1; balance_cpu = i; } + + load = target_load(i, load_idx); } else { load = source_load(i, load_idx); if (load > max_cpu_load) { @@ -3824,8 +3824,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, */ if (local_group) { if (env->idle != CPU_NEWLY_IDLE) { - if (balance_cpu != env->dst_cpu || - cmpxchg(&group->balance_cpu, -1, balance_cpu) != -1) { + if (balance_cpu != env->dst_cpu) { *balance = 0; return; } @@ -4919,7 +4918,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle) int balance = 1; struct rq *rq = cpu_rq(cpu); unsigned long interval; - struct sched_domain *sd, *last = NULL; + struct sched_domain *sd; /* Earliest time when we have to do rebalance again */ unsigned long next_balance = jiffies + 60*HZ; int update_next_balance = 0; @@ -4929,7 +4928,6 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle) rcu_read_lock(); for_each_domain(cpu, sd) { - last = sd; if (!(sd->flags & SD_LOAD_BALANCE)) continue; @@ -4974,9 +4972,6 @@ out: if (!balance) break; } - for (sd = last; sd; sd = sd->child) - (void)cmpxchg(&sd->groups->balance_cpu, cpu, -1); - rcu_read_unlock(); /* -- cgit v1.2.3