Messages in this thread Patch in this message | | | Subject | Re: load balancing regression since commit 367456c7 | From | Peter Zijlstra <> | Date | Tue, 17 Apr 2012 13:43:33 +0200 |
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On Tue, 2012-04-10 at 18:06 -0700, Tim Chen wrote: > Peter, > > We noticed in a hackbench test (./hackbench 100 process 2000) > on a Sandy bridge 2 socket server, there has been a slow down > by a factor of 4 since commit 367456c7 was applied > (sched: Ditch per cgroup task lists for load-balancing). > > The commit 5d6523e (sched: Fix load-balance wreckage) did > not fix the regression. > > In the profile, there is heavy spin lock contention in the load_balance path of 3.4-rc2 > where it was less than .003% of cpu before commit 367456c7.
I can't actually reproduce but does the below help?
If not, can you shoot your .config over?
--- kernel/sched/fair.c | 8 +++++--- 1 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0d97ebd..e1da5c6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3215,6 +3215,8 @@ static int move_one_task(struct lb_env *env) static unsigned long task_h_load(struct task_struct *p); +static const unsigned int sched_nr_migrate_break = IS_ENABLED(CONFIG_PREEMPT) ? 8 : 32; + /* * move_tasks tries to move up to load_move weighted load from busiest to * this_rq, as part of a balancing operation within domain "sd". @@ -3242,7 +3244,7 @@ static int move_tasks(struct lb_env *env) /* take a breather every nr_migrate tasks */ if (env->loop > env->loop_break) { - env->loop_break += sysctl_sched_nr_migrate; + env->loop_break += sched_nr_migrate_break; env->flags |= LBF_NEED_BREAK; break; } @@ -4407,7 +4409,8 @@ static int load_balance(int this_cpu, struct rq *this_rq, .dst_cpu = this_cpu, .dst_rq = this_rq, .idle = idle, - .loop_break = sysctl_sched_nr_migrate, + .loop_break = sched_nr_migrate_break, + .loop_max = sysctl_sched_nr_migrate, }; cpumask_copy(cpus, cpu_active_mask); @@ -4448,7 +4451,6 @@ static int load_balance(int this_cpu, struct rq *this_rq, env.load_move = imbalance; env.src_cpu = busiest->cpu; env.src_rq = busiest; - env.loop_max = busiest->nr_running; more_balance: local_irq_save(flags);
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