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Date: Thu, 6 May 2021 22:15:38 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Mel Gorman <mgorman@...hsingularity.net>,
Rik van Riel <riel@...riel.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Valentin Schneider <valentin.schneider@....com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
Parth Shah <parth@...ux.ibm.com>
Subject: [PATCH v2 3/8] sched/fair: Update idle-core more often
Currently when the scheduler does a load balance and pulls a task or
when a CPU picks up a task during wakeup without having to call
select_idle_cpu(), it never checks if the target CPU is part of the
idle-core. This makes idle-core less accurate.
Given that the identity of idle-core for LLC is maintained, its easy to
update the idle-core as soon as the CPU picks up a task.
This change will update the idle-core whenever a CPU from the idle-core
picks up a task. However if there are multiple idle-cores in the LLC,
and waking CPU happens to be part of the designated idle-core, idle-core
is set to -1. In cases where the scheduler is sure that there are no
more idle-cores, idle-core is set to -2.
To reduce this case, whenever a CPU updates idle-core, it will look for
other cores in the LLC for an idle-core, if the core to which it belongs
to is not idle.
Cc: LKML <linux-kernel@...r.kernel.org>
Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc: Parth Shah <parth@...ux.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Rik van Riel <riel@...riel.com>
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
---
kernel/sched/fair.c | 54 +++++++++++++++++++++++++++++++++++++++++---
kernel/sched/idle.c | 6 +++++
kernel/sched/sched.h | 2 ++
3 files changed, 59 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8c9d1a210820..50da2363317d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6015,6 +6015,13 @@ static inline int __select_idle_cpu(int cpu)
DEFINE_STATIC_KEY_FALSE(sched_smt_present);
EXPORT_SYMBOL_GPL(sched_smt_present);
+/*
+ * Value of -2 indicates there are no idle-cores in LLC.
+ * Value of -1 indicates an idle-core turned to busy recently.
+ * However there could be other idle-cores in the system.
+ * Anyother value indicates core to which the CPU(value)
+ * belongs is idle.
+ */
static inline void set_idle_core(int cpu, int val)
{
struct sched_domain_shared *sds;
@@ -6037,6 +6044,40 @@ static inline int get_idle_core(int cpu, int def)
return def;
}
+static void set_next_idle_core(struct sched_domain *sd, int target)
+{
+ struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
+ int core, cpu;
+
+ cpumask_andnot(cpus, sched_domain_span(sd), cpu_smt_mask(target));
+ for_each_cpu_wrap(core, cpus, target) {
+ bool idle = true;
+
+ for_each_cpu(cpu, cpu_smt_mask(core)) {
+ if (!available_idle_cpu(cpu)) {
+ idle = false;
+ break;
+ }
+ }
+
+ if (idle) {
+ set_idle_core(core, per_cpu(smt_id, core));
+ return;
+ }
+
+ cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
+ }
+ set_idle_core(target, -2);
+}
+
+void set_core_busy(int core)
+{
+ rcu_read_lock();
+ if (get_idle_core(core, -1) == per_cpu(smt_id, core))
+ set_idle_core(core, -1);
+ rcu_read_unlock();
+}
+
/*
* Scans the local SMT mask to see if the entire core is idle, and records this
* information in sd_llc_shared->idle_core.
@@ -6046,11 +6087,13 @@ static inline int get_idle_core(int cpu, int def)
*/
void __update_idle_core(struct rq *rq)
{
+ struct sched_domain *sd;
int core = cpu_of(rq);
int cpu;
rcu_read_lock();
- if (get_idle_core(core, 0) >= 0)
+ sd = rcu_dereference(per_cpu(sd_llc, core));
+ if (!sd || get_idle_core(core, 0) >= 0)
goto unlock;
for_each_cpu(cpu, cpu_smt_mask(core)) {
@@ -6058,10 +6101,15 @@ void __update_idle_core(struct rq *rq)
continue;
if (!available_idle_cpu(cpu))
- goto unlock;
+ goto try_next;
}
set_idle_core(core, per_cpu(smt_id, core));
+ goto unlock;
+
+try_next:
+ set_next_idle_core(sd, core);
+
unlock:
rcu_read_unlock();
}
@@ -6130,7 +6178,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
int i, cpu, idle_cpu = -1, nr = INT_MAX;
int idle_core = get_idle_core(target, -1);
- bool smt = (idle_core != -1);
+ bool smt = (idle_core != -2);
int this = smp_processor_id();
struct sched_domain *this_sd;
u64 time;
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 7199e6f23789..cc828f3efe71 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -425,6 +425,12 @@ static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int fl
static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
{
+#ifdef CONFIG_SCHED_SMT
+ int cpu = rq->cpu;
+
+ if (static_branch_likely(&sched_smt_present))
+ set_core_busy(cpu);
+#endif
}
static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 46d40a281724..5c0bd4b0e73a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1102,6 +1102,7 @@ static inline bool is_migration_disabled(struct task_struct *p)
#ifdef CONFIG_SCHED_SMT
extern void __update_idle_core(struct rq *rq);
+extern void set_core_busy(int cpu);
static inline void update_idle_core(struct rq *rq)
{
@@ -1111,6 +1112,7 @@ static inline void update_idle_core(struct rq *rq)
#else
static inline void update_idle_core(struct rq *rq) { }
+static inline void set_core_busy(int cpu) { }
#endif
DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
--
2.18.2
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