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Subject[PATCH v5 1/2] sched/deadline: optimize sched_dl_global_validate()
Under CONFIG_SMP, dl_bw is per root domain, but not per CPU.
When checking or updating dl_bw, currently iterating every CPU is
overdoing, just need iterate each root domain once.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Peng Liu <iwtbavbm@gmail.com>
---
kernel/sched/deadline.c | 43 ++++++++++++++++++++++++++++++++---------
kernel/sched/sched.h | 7 +++++++
kernel/sched/topology.c | 1 +
3 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index c19c1883d695..5200e185923f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -97,6 +97,17 @@ static inline unsigned long dl_bw_capacity(int i)
return __dl_bw_capacity(i);
}
}
+
+static inline bool dl_bw_visited(int cpu, u32 gen)
+{
+ struct root_domain *rd = cpu_rq(cpu)->rd;
+
+ if (rd->visit_gen == gen)
+ return true;
+
+ rd->visit_gen = gen;
+ return false;
+}
#else
static inline struct dl_bw *dl_bw_of(int i)
{
@@ -112,6 +123,11 @@ static inline unsigned long dl_bw_capacity(int i)
{
return SCHED_CAPACITY_SCALE;
}
+
+static inline bool dl_bw_visited(int cpu, u32 gen)
+{
+ return false;
+}
#endif

static inline
@@ -2514,26 +2530,30 @@ const struct sched_class dl_sched_class
.update_curr = update_curr_dl,
};

+/* Used for dl_bw check and update. */
+static u32 dl_generation;
+
int sched_dl_global_validate(void)
{
u64 runtime = global_rt_runtime();
u64 period = global_rt_period();
u64 new_bw = to_ratio(period, runtime);
struct dl_bw *dl_b;
- int cpu, ret = 0;
unsigned long flags;
+ int cpu, ret = 0;
+ u32 gen = ++dl_generation;

/*
* Here we want to check the bandwidth not being set to some
* value smaller than the currently allocated bandwidth in
* any of the root_domains.
- *
- * FIXME: Cycling on all the CPUs is overdoing, but simpler than
- * cycling on root_domains... Discussion on different/better
- * solutions is welcome!
*/
for_each_possible_cpu(cpu) {
rcu_read_lock_sched();
+
+ if (dl_bw_visited(cpu, gen))
+ goto next;
+
dl_b = dl_bw_of(cpu);

raw_spin_lock_irqsave(&dl_b->lock, flags);
@@ -2541,6 +2561,7 @@ int sched_dl_global_validate(void)
ret = -EBUSY;
raw_spin_unlock_irqrestore(&dl_b->lock, flags);

+next:
rcu_read_unlock_sched();

if (ret)
@@ -2567,8 +2588,9 @@ void sched_dl_do_global(void)
{
u64 new_bw = -1;
struct dl_bw *dl_b;
- int cpu;
unsigned long flags;
+ int cpu;
+ u32 gen = ++dl_generation;

def_dl_bandwidth.dl_period = global_rt_period();
def_dl_bandwidth.dl_runtime = global_rt_runtime();
@@ -2576,11 +2598,14 @@ void sched_dl_do_global(void)
if (global_rt_runtime() != RUNTIME_INF)
new_bw = to_ratio(global_rt_period(), global_rt_runtime());

- /*
- * FIXME: As above...
- */
for_each_possible_cpu(cpu) {
rcu_read_lock_sched();
+
+ if (dl_bw_visited(cpu, gen)) {
+ rcu_read_unlock_sched();
+ continue;
+ }
+
dl_b = dl_bw_of(cpu);

raw_spin_lock_irqsave(&dl_b->lock, flags);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 28709f6b0975..53477e8b26b0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -798,6 +798,13 @@ struct root_domain {
*/
cpumask_var_t dlo_mask;
atomic_t dlo_count;
+
+ /*
+ * Indicate whether a root_domain's dl_bw has been checked or
+ * updated. It's monotonously increasing, then wrap around.
+ */
+ u32 visit_gen;
+
struct dl_bw dl_bw;
struct cpudl cpudl;

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index dd7770226086..90f3e5558fa2 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -516,6 +516,7 @@ static int init_rootdomain(struct root_domain *rd)
init_irq_work(&rd->rto_push_work, rto_push_irq_work_func);
#endif

+ rd->visit_gen = 0;
init_dl_bw(&rd->dl_bw);
if (cpudl_init(&rd->cpudl) != 0)
goto free_rto_mask;
--
2.20.1
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