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Date: Mon, 23 Apr 2018 17:41:14 -0700
From: subhra mazumdar <subhra.mazumdar@...cle.com>
To: linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, mingo@...hat.com, daniel.lezcano@...aro.org,
steven.sistare@...cle.com, dhaval.giani@...cle.com,
rohit.k.jain@...cle.com, subhra.mazumdar@...cle.com
Subject: [PATCH 1/3] sched: remove select_idle_core() for scalability
select_idle_core() can potentially search all cpus to find the fully idle
core even if there is one such core. Removing this is necessary to achieve
scalability in the fast path.
Signed-off-by: subhra mazumdar <subhra.mazumdar@...cle.com>
---
include/linux/sched/topology.h | 1 -
kernel/sched/fair.c | 97 ------------------------------------------
kernel/sched/idle.c | 1 -
kernel/sched/sched.h | 10 -----
4 files changed, 109 deletions(-)
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 2634774..ac7944d 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -71,7 +71,6 @@ struct sched_group;
struct sched_domain_shared {
atomic_t ref;
atomic_t nr_busy_cpus;
- int has_idle_cores;
};
struct sched_domain {
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 54dc31e..d1d4769 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6239,94 +6239,6 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
#ifdef CONFIG_SCHED_SMT
-static inline void set_idle_cores(int cpu, int val)
-{
- struct sched_domain_shared *sds;
-
- sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
- if (sds)
- WRITE_ONCE(sds->has_idle_cores, val);
-}
-
-static inline bool test_idle_cores(int cpu, bool def)
-{
- struct sched_domain_shared *sds;
-
- sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
- if (sds)
- return READ_ONCE(sds->has_idle_cores);
-
- return def;
-}
-
-/*
- * Scans the local SMT mask to see if the entire core is idle, and records this
- * information in sd_llc_shared->has_idle_cores.
- *
- * Since SMT siblings share all cache levels, inspecting this limited remote
- * state should be fairly cheap.
- */
-void __update_idle_core(struct rq *rq)
-{
- int core = cpu_of(rq);
- int cpu;
-
- rcu_read_lock();
- if (test_idle_cores(core, true))
- goto unlock;
-
- for_each_cpu(cpu, cpu_smt_mask(core)) {
- if (cpu == core)
- continue;
-
- if (!idle_cpu(cpu))
- goto unlock;
- }
-
- set_idle_cores(core, 1);
-unlock:
- rcu_read_unlock();
-}
-
-/*
- * Scan the entire LLC domain for idle cores; this dynamically switches off if
- * there are no idle cores left in the system; tracked through
- * sd_llc->shared->has_idle_cores and enabled through update_idle_core() above.
- */
-static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
-{
- struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
- int core, cpu;
-
- if (!static_branch_likely(&sched_smt_present))
- return -1;
-
- if (!test_idle_cores(target, false))
- return -1;
-
- cpumask_and(cpus, sched_domain_span(sd), &p->cpus_allowed);
-
- for_each_cpu_wrap(core, cpus, target) {
- bool idle = true;
-
- for_each_cpu(cpu, cpu_smt_mask(core)) {
- cpumask_clear_cpu(cpu, cpus);
- if (!idle_cpu(cpu))
- idle = false;
- }
-
- if (idle)
- return core;
- }
-
- /*
- * Failed to find an idle core; stop looking for one.
- */
- set_idle_cores(target, 0);
-
- return -1;
-}
-
/*
* Scan the local SMT mask for idle CPUs.
*/
@@ -6349,11 +6261,6 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t
#else /* CONFIG_SCHED_SMT */
-static inline int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
-{
- return -1;
-}
-
static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
{
return -1;
@@ -6451,10 +6358,6 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
if (!sd)
return target;
- i = select_idle_core(p, sd, target);
- if ((unsigned)i < nr_cpumask_bits)
- return i;
-
i = select_idle_cpu(p, sd, target);
if ((unsigned)i < nr_cpumask_bits)
return i;
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 1a3e9bd..7ca8e18 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -392,7 +392,6 @@ static struct task_struct *
pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
put_prev_task(rq, prev);
- update_idle_core(rq);
schedstat_inc(rq->sched_goidle);
return rq->idle;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 15750c2..3f1874c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -899,16 +899,6 @@ static inline int cpu_of(struct rq *rq)
extern struct static_key_false sched_smt_present;
-extern void __update_idle_core(struct rq *rq);
-
-static inline void update_idle_core(struct rq *rq)
-{
- if (static_branch_unlikely(&sched_smt_present))
- __update_idle_core(rq);
-}
-
-#else
-static inline void update_idle_core(struct rq *rq) { }
#endif
DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
--
2.9.3
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