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Date: Thu, 29 Oct 2020 10:51:51 -0000
From: "tip-bot2 for Peng Liu" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
Peng Liu <iwtbavbm@...il.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>, x86 <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/core] sched/deadline: Optimize sched_dl_global_validate()
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 26762423a2664692de2bcccc9de684a5ac105e23
Gitweb: https://git.kernel.org/tip/26762423a2664692de2bcccc9de684a5ac105e23
Author: Peng Liu <iwtbavbm@...il.com>
AuthorDate: Thu, 08 Oct 2020 23:48:46 +08:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 29 Oct 2020 11:00:28 +01:00
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@...radead.org>
Signed-off-by: Peng Liu <iwtbavbm@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Acked-by: Juri Lelli <juri.lelli@...hat.com>
Link: https://lkml.kernel.org/r/78d21ee792cc48ff79e8cd62a5f26208463684d6.1602171061.git.iwtbavbm@gmail.com
---
kernel/sched/deadline.c | 39 ++++++++++++++++++++++++++++++++-------
kernel/sched/sched.h | 9 +++++++++
kernel/sched/topology.c | 1 +
3 files changed, 42 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index f232305..98d96d4 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, u64 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, u64 gen)
+{
+ return false;
+}
#endif
static inline
@@ -2535,11 +2551,15 @@ const struct sched_class dl_sched_class
.update_curr = update_curr_dl,
};
+/* Used for dl_bw check and update, used under sched_rt_handler()::mutex */
+static u64 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);
+ u64 gen = ++dl_generation;
struct dl_bw *dl_b;
int cpu, ret = 0;
unsigned long flags;
@@ -2548,13 +2568,13 @@ int sched_dl_global_validate(void)
* 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);
@@ -2562,6 +2582,7 @@ int sched_dl_global_validate(void)
ret = -EBUSY;
raw_spin_unlock_irqrestore(&dl_b->lock, flags);
+next:
rcu_read_unlock_sched();
if (ret)
@@ -2587,6 +2608,7 @@ static void init_dl_rq_bw_ratio(struct dl_rq *dl_rq)
void sched_dl_do_global(void)
{
u64 new_bw = -1;
+ u64 gen = ++dl_generation;
struct dl_bw *dl_b;
int cpu;
unsigned long flags;
@@ -2597,11 +2619,14 @@ 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 df80bfc..49a2dae 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -801,6 +801,15 @@ struct root_domain {
struct dl_bw dl_bw;
struct cpudl cpudl;
+ /*
+ * Indicate whether a root_domain's dl_bw has been checked or
+ * updated. It's monotonously increasing value.
+ *
+ * Also, some corner cases, like 'wrap around' is dangerous, but given
+ * that u64 is 'big enough'. So that shouldn't be a concern.
+ */
+ u64 visit_gen;
+
#ifdef HAVE_RT_PUSH_IPI
/*
* For IPI pull requests, loop across the rto_mask.
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index dd77702..90f3e55 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;
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