>From ca30caf20c706ba4d5351252c68b4e6a74cef25f Mon Sep 17 00:00:00 2001 From: Chris Redpath Date: Thu, 9 May 2013 16:21:15 +0100 Subject: HMP: Select least-loaded CPU when performing HMP Migrations The reference patch set always selects the first CPU in an HMP domain as a migration target. In busy situations, this means that the migrated thread cannot make immediate use of an idle CPU but must share a busy one until the load balancer runs across the big domain. This patch uses the hmp_domain_min_load function introduced in global balancing to figure out which of the CPUs is the least busy and selects that as a migration target - in both directions. This essentially implements a task-spread strategy and is intended to maximise performance of migrated threads but is likely to use more power than the packing strategy previously employed. Signed-off-by: Chris Redpath Signed-off-by: Liviu Dudau --- kernel/sched/fair.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a90a638..d7303c5 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3598,6 +3598,8 @@ unsigned int hmp_next_down_threshold = 4096; static unsigned int hmp_up_migration(int cpu, struct sched_entity *se); static unsigned int hmp_down_migration(int cpu, struct sched_entity *se); +static inline unsigned int hmp_domain_min_load(struct hmp_domain *hmpd, + int *min_cpu); /* Check if cpu is in fastest hmp_domain */ static inline unsigned int hmp_cpu_is_fastest(int cpu) @@ -3642,7 +3644,16 @@ static inline struct hmp_domain *hmp_faster_domain(int cpu) static inline unsigned int hmp_select_faster_cpu(struct task_struct *tsk, int cpu) { - return cpumask_any_and(&hmp_faster_domain(cpu)->cpus, + int lowest_cpu=NR_CPUS; + __always_unused int lowest_ratio = hmp_domain_min_load(hmp_faster_domain(cpu), &lowest_cpu); + /* + * If the lowest-loaded CPU in the domain is allowed by the task affinity + * select that one, otherwise select one which is allowed + */ + if(lowest_cpu != NR_CPUS && cpumask_test_cpu(lowest_cpu,tsk_cpus_allowed(tsk))) + return lowest_cpu; + else + return cpumask_any_and(&hmp_faster_domain(cpu)->cpus, tsk_cpus_allowed(tsk)); } @@ -3653,7 +3664,16 @@ static inline unsigned int hmp_select_faster_cpu(struct task_struct *tsk, static inline unsigned int hmp_select_slower_cpu(struct task_struct *tsk, int cpu) { - return cpumask_any_and(&hmp_slower_domain(cpu)->cpus, + int lowest_cpu=NR_CPUS; + __always_unused int lowest_ratio = hmp_domain_min_load(hmp_slower_domain(cpu), &lowest_cpu); + /* + * If the lowest-loaded CPU in the domain is allowed by the task affinity + * select that one, otherwise select one which is allowed + */ + if(lowest_cpu != NR_CPUS && cpumask_test_cpu(lowest_cpu,tsk_cpus_allowed(tsk))) + return lowest_cpu; + else + return cpumask_any_and(&hmp_slower_domain(cpu)->cpus, tsk_cpus_allowed(tsk)); } -- 1.7.9.5