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sched: Prevent to re-select dst-cpu in load_balance() 

Commit 88b8dac0 makes load_balance() consider other cpus in its
group. But, in that, there is no code for preventing to
re-select dst-cpu. So, same dst-cpu can be selected over and
over.

This patch add functionality to load_balance() in order to
exclude cpu which is selected once. We prevent to re-select
dst_cpu via env's cpus, so now, env's cpus is a candidate not
only for src_cpus, but also dst_cpus.

With this patch, we can remove lb_iterations and
max_lb_iterations, because we decide whether we can go ahead or
not via env's cpus.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Jason Low <jason.low2@hp.com>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1366705662-3587-7-git-send-email-iamjoonsoo.kim@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Joonsoo Kim 2013-04-23 17:27:42 +09:00 committed by Ingo Molnar
parent e6252c3ef4
commit e02e60c109
1 changed files with 15 additions and 18 deletions
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33
kernel/sched/fair.c
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@ -3905,7 +3905,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
return 0;
if (!cpumask_test_cpu(env->dst_cpu, tsk_cpus_allowed(p))) {
int new_dst_cpu;
int cpu;
schedstat_inc(p, se.statistics.nr_failed_migrations_affine);
@ -3920,12 +3920,15 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
if (!env->dst_grpmask || (env->flags & LBF_SOME_PINNED))
return 0;
new_dst_cpu = cpumask_first_and(env->dst_grpmask,
tsk_cpus_allowed(p));
if (new_dst_cpu < nr_cpu_ids) {
env->flags |= LBF_SOME_PINNED;
env->new_dst_cpu = new_dst_cpu;
/* Prevent to re-select dst_cpu via env's cpus */
for_each_cpu_and(cpu, env->dst_grpmask, env->cpus) {
if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) {
env->flags |= LBF_SOME_PINNED;
env->new_dst_cpu = cpu;
break;
}
}
return 0;
}
@ -5008,7 +5011,6 @@ static int load_balance(int this_cpu, struct rq *this_rq,
int *balance)
{
int ld_moved, cur_ld_moved, active_balance = 0;
int lb_iterations, max_lb_iterations;
struct sched_group *group;
struct rq *busiest;
unsigned long flags;
@ -5028,15 +5030,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
* For NEWLY_IDLE load_balancing, we don't need to consider
* other cpus in our group
*/
if (idle == CPU_NEWLY_IDLE) {
if (idle == CPU_NEWLY_IDLE)
env.dst_grpmask = NULL;
/*
* we don't care max_lb_iterations in this case,
* in following patch, this will be removed
*/
max_lb_iterations = 0;
} else
max_lb_iterations = cpumask_weight(env.dst_grpmask);
cpumask_copy(cpus, cpu_active_mask);
@ -5064,7 +5059,6 @@ redo:
schedstat_add(sd, lb_imbalance[idle], env.imbalance);
ld_moved = 0;
lb_iterations = 1;
if (busiest->nr_running > 1) {
/*
* Attempt to move tasks. If find_busiest_group has found
@ -5121,14 +5115,17 @@ more_balance:
* moreover subsequent load balance cycles should correct the
* excess load moved.
*/
if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0 &&
lb_iterations++ < max_lb_iterations) {
if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0) {
env.dst_rq = cpu_rq(env.new_dst_cpu);
env.dst_cpu = env.new_dst_cpu;
env.flags &= ~LBF_SOME_PINNED;
env.loop = 0;
env.loop_break = sched_nr_migrate_break;
/* Prevent to re-select dst_cpu via env's cpus */
cpumask_clear_cpu(env.dst_cpu, env.cpus);
/*
* Go back to "more_balance" rather than "redo" since we
* need to continue with same src_cpu.