[PATCH v4 0/5] sched/fair: Minor SIS optimizations

[PATCH v4 0/5] sched/fair: Minor SIS optimizations

[Abel Wu]

v4:
 - Fomat fixes
 - Collect Acked-Bys from Mel

v3:
 - Fix an uninitialised memory access issue which can happen when switching SIS_PROP

v2:
 - Removed the part ignoring SIS_UTIL when overloaded
 - Make SIS_PROP cleanup a separate patch
 - Collect Acked-Bys from Mel

Abel Wu (5):
  sched/fair: Remove redundant check in select_idle_smt()
  sched/fair: Avoid double search on same cpu
  sched/fair: Remove useless check in select_idle_core()
  sched/fair: Default to false in test_idle_cores()
  sched/fair: Cleanup for SIS_PROP

 kernel/sched/fair.c | 42 +++++++++++++++++++-----------------------
 1 file changed, 19 insertions(+), 23 deletions(-)

-- 
2.37.3

[PATCH v4 1/5] sched/fair: Remove redundant check in select_idle_smt()

[Abel Wu]

If two cpus share LLC cache, then the two cores they belong to
are also in the same LLC domain.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Reviewed-by: Josh Don <joshdon@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
---
 kernel/sched/fair.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index efceb670e755..9657c7de5f57 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6350,14 +6350,11 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 /*
  * Scan the local SMT mask for idle CPUs.
  */
-static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
+static int select_idle_smt(struct task_struct *p, int target)
 {
 	int cpu;
 
-	for_each_cpu(cpu, cpu_smt_mask(target)) {
-		if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
-		    !cpumask_test_cpu(cpu, sched_domain_span(sd)))
-			continue;
+	for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
 		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
 			return cpu;
 	}
@@ -6381,7 +6378,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
 	return __select_idle_cpu(core, p);
 }
 
-static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
+static inline int select_idle_smt(struct task_struct *p, int target)
 {
 	return -1;
 }
@@ -6615,7 +6612,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 		has_idle_core = test_idle_cores(target, false);
 
 		if (!has_idle_core && cpus_share_cache(prev, target)) {
-			i = select_idle_smt(p, sd, prev);
+			i = select_idle_smt(p, prev);
 			if ((unsigned int)i < nr_cpumask_bits)
 				return i;
 		}
-- 
2.37.3

[tip: sched/core] sched/fair: Remove redundant check in select_idle_smt()

[tip-bot2 for Abel Wu]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     3e6efe87cd5ccabf0f1d4e3ef25881ca0fd337e7
Gitweb:        https://git.kernel.org/tip/3e6efe87cd5ccabf0f1d4e3ef25881ca0fd337e7
Author:        Abel Wu <wuyun.abel@bytedance.com>
AuthorDate:    Wed, 07 Sep 2022 19:19:56 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 07 Sep 2022 21:53:46 +02:00

sched/fair: Remove redundant check in select_idle_smt()

If two cpus share LLC cache, then the two cores they belong to
are also in the same LLC domain.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Don <joshdon@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/20220907112000.1854-2-wuyun.abel@bytedance.com
---
 kernel/sched/fair.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index efceb67..9657c7d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6350,14 +6350,11 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 /*
  * Scan the local SMT mask for idle CPUs.
  */
-static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
+static int select_idle_smt(struct task_struct *p, int target)
 {
 	int cpu;
 
-	for_each_cpu(cpu, cpu_smt_mask(target)) {
-		if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
-		    !cpumask_test_cpu(cpu, sched_domain_span(sd)))
-			continue;
+	for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
 		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
 			return cpu;
 	}
@@ -6381,7 +6378,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
 	return __select_idle_cpu(core, p);
 }
 
-static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
+static inline int select_idle_smt(struct task_struct *p, int target)
 {
 	return -1;
 }
@@ -6615,7 +6612,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 		has_idle_core = test_idle_cores(target, false);
 
 		if (!has_idle_core && cpus_share_cache(prev, target)) {
-			i = select_idle_smt(p, sd, prev);
+			i = select_idle_smt(p, prev);
 			if ((unsigned int)i < nr_cpumask_bits)
 				return i;
 		}

[PATCH v4 2/5] sched/fair: Avoid double search on same cpu

[Abel Wu]

The prev cpu is checked at the beginning of SIS, and it's unlikely
to be idle before the second check in select_idle_smt(). So we'd
better focus on its SMT siblings.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Reviewed-by: Josh Don <joshdon@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9657c7de5f57..1ad79aaaaf93 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6355,6 +6355,8 @@ static int select_idle_smt(struct task_struct *p, int target)
 	int cpu;
 
 	for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
+		if (cpu == target)
+			continue;
 		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
 			return cpu;
 	}
-- 
2.37.3

[tip: sched/core] sched/fair: Avoid double search on same cpu

[tip-bot2 for Abel Wu]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     b9bae70440d21e106fbc098803b5a190df65f2e0
Gitweb:        https://git.kernel.org/tip/b9bae70440d21e106fbc098803b5a190df65f2e0
Author:        Abel Wu <wuyun.abel@bytedance.com>
AuthorDate:    Wed, 07 Sep 2022 19:19:57 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 07 Sep 2022 21:53:46 +02:00

sched/fair: Avoid double search on same cpu

The prev cpu is checked at the beginning of SIS, and it's unlikely
to be idle before the second check in select_idle_smt(). So we'd
better focus on its SMT siblings.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Don <joshdon@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/20220907112000.1854-3-wuyun.abel@bytedance.com
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9657c7d..1ad79aa 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6355,6 +6355,8 @@ static int select_idle_smt(struct task_struct *p, int target)
 	int cpu;
 
 	for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
+		if (cpu == target)
+			continue;
 		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
 			return cpu;
 	}

[PATCH v4 3/5] sched/fair: Remove useless check in select_idle_core()

[Abel Wu]

The function select_idle_core() only gets called when has_idle_cores
is true which can be possible only when sched_smt_present is enabled.

This change also aligns select_idle_core() with select_idle_smt() in
the way that the caller do the check if necessary.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
---
 kernel/sched/fair.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1ad79aaaaf93..03ce65068333 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6321,9 +6321,6 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 	bool idle = true;
 	int cpu;
 
-	if (!static_branch_likely(&sched_smt_present))
-		return __select_idle_cpu(core, p);
-
 	for_each_cpu(cpu, cpu_smt_mask(core)) {
 		if (!available_idle_cpu(cpu)) {
 			idle = false;
-- 
2.37.3

[tip: sched/core] sched/fair: Remove useless check in select_idle_core()

[tip-bot2 for Abel Wu]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     8eeeed9c4a791f0d1f2ea830eb75a4246c117ae2
Gitweb:        https://git.kernel.org/tip/8eeeed9c4a791f0d1f2ea830eb75a4246c117ae2
Author:        Abel Wu <wuyun.abel@bytedance.com>
AuthorDate:    Wed, 07 Sep 2022 19:19:58 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 07 Sep 2022 21:53:46 +02:00

sched/fair: Remove useless check in select_idle_core()

The function select_idle_core() only gets called when has_idle_cores
is true which can be possible only when sched_smt_present is enabled.

This change also aligns select_idle_core() with select_idle_smt() in
the way that the caller do the check if necessary.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/20220907112000.1854-4-wuyun.abel@bytedance.com
---
 kernel/sched/fair.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1ad79aa..03ce650 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6321,9 +6321,6 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 	bool idle = true;
 	int cpu;
 
-	if (!static_branch_likely(&sched_smt_present))
-		return __select_idle_cpu(core, p);
-
 	for_each_cpu(cpu, cpu_smt_mask(core)) {
 		if (!available_idle_cpu(cpu)) {
 			idle = false;

[PATCH v4 4/5] sched/fair: Default to false in test_idle_cores()

[Abel Wu]

It's uncertain whether idle cores exist or not if shared sched-
domains are not ready, so returning "no idle cores" usually
makes sense.

While __update_idle_core() is an exception, it checks status
of this core and set hint to shared sched-domain if necessary.
So the whole logic of this function depends on the existence
of shared sched-domain, and can certainly bail out early if
it is not available.

It's somehow a little tricky, and as Josh suggested that it
should be transient while the domain isn't ready. So remove
the self-defined default value to make things more clearer.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Reviewed-by: Josh Don <joshdon@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
---
 kernel/sched/fair.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 03ce65068333..23b020c3d3a0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1588,11 +1588,11 @@ numa_type numa_classify(unsigned int imbalance_pct,
 
 #ifdef CONFIG_SCHED_SMT
 /* Forward declarations of select_idle_sibling helpers */
-static inline bool test_idle_cores(int cpu, bool def);
+static inline bool test_idle_cores(int cpu);
 static inline int numa_idle_core(int idle_core, int cpu)
 {
 	if (!static_branch_likely(&sched_smt_present) ||
-	    idle_core >= 0 || !test_idle_cores(cpu, false))
+	    idle_core >= 0 || !test_idle_cores(cpu))
 		return idle_core;
 
 	/*
@@ -6271,7 +6271,7 @@ static inline void set_idle_cores(int cpu, int val)
 		WRITE_ONCE(sds->has_idle_cores, val);
 }
 
-static inline bool test_idle_cores(int cpu, bool def)
+static inline bool test_idle_cores(int cpu)
 {
 	struct sched_domain_shared *sds;
 
@@ -6279,7 +6279,7 @@ static inline bool test_idle_cores(int cpu, bool def)
 	if (sds)
 		return READ_ONCE(sds->has_idle_cores);
 
-	return def;
+	return false;
 }
 
 /*
@@ -6295,7 +6295,7 @@ void __update_idle_core(struct rq *rq)
 	int cpu;
 
 	rcu_read_lock();
-	if (test_idle_cores(core, true))
+	if (test_idle_cores(core))
 		goto unlock;
 
 	for_each_cpu(cpu, cpu_smt_mask(core)) {
@@ -6367,9 +6367,9 @@ static inline void set_idle_cores(int cpu, int val)
 {
 }
 
-static inline bool test_idle_cores(int cpu, bool def)
+static inline bool test_idle_cores(int cpu)
 {
-	return def;
+	return false;
 }
 
 static inline int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
@@ -6608,7 +6608,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 		return target;
 
 	if (sched_smt_active()) {
-		has_idle_core = test_idle_cores(target, false);
+		has_idle_core = test_idle_cores(target);
 
 		if (!has_idle_core && cpus_share_cache(prev, target)) {
 			i = select_idle_smt(p, prev);
-- 
2.37.3

[tip: sched/core] sched/fair: Default to false in test_idle_cores()

[tip-bot2 for Abel Wu]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     398ba2b0cc0a43964fe3d2dd19cb2a478f1f220b
Gitweb:        https://git.kernel.org/tip/398ba2b0cc0a43964fe3d2dd19cb2a478f1f220b
Author:        Abel Wu <wuyun.abel@bytedance.com>
AuthorDate:    Wed, 07 Sep 2022 19:19:59 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 07 Sep 2022 21:53:47 +02:00

sched/fair: Default to false in test_idle_cores()

It's uncertain whether idle cores exist or not if shared sched-
domains are not ready, so returning "no idle cores" usually
makes sense.

While __update_idle_core() is an exception, it checks status
of this core and set hint to shared sched-domain if necessary.
So the whole logic of this function depends on the existence
of shared sched-domain, and can certainly bail out early if
it is not available.

It's somehow a little tricky, and as Josh suggested that it
should be transient while the domain isn't ready. So remove
the self-defined default value to make things more clearer.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Don <joshdon@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/20220907112000.1854-5-wuyun.abel@bytedance.com
---
 kernel/sched/fair.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 03ce650..23b020c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1588,11 +1588,11 @@ numa_type numa_classify(unsigned int imbalance_pct,
 
 #ifdef CONFIG_SCHED_SMT
 /* Forward declarations of select_idle_sibling helpers */
-static inline bool test_idle_cores(int cpu, bool def);
+static inline bool test_idle_cores(int cpu);
 static inline int numa_idle_core(int idle_core, int cpu)
 {
 	if (!static_branch_likely(&sched_smt_present) ||
-	    idle_core >= 0 || !test_idle_cores(cpu, false))
+	    idle_core >= 0 || !test_idle_cores(cpu))
 		return idle_core;
 
 	/*
@@ -6271,7 +6271,7 @@ static inline void set_idle_cores(int cpu, int val)
 		WRITE_ONCE(sds->has_idle_cores, val);
 }
 
-static inline bool test_idle_cores(int cpu, bool def)
+static inline bool test_idle_cores(int cpu)
 {
 	struct sched_domain_shared *sds;
 
@@ -6279,7 +6279,7 @@ static inline bool test_idle_cores(int cpu, bool def)
 	if (sds)
 		return READ_ONCE(sds->has_idle_cores);
 
-	return def;
+	return false;
 }
 
 /*
@@ -6295,7 +6295,7 @@ void __update_idle_core(struct rq *rq)
 	int cpu;
 
 	rcu_read_lock();
-	if (test_idle_cores(core, true))
+	if (test_idle_cores(core))
 		goto unlock;
 
 	for_each_cpu(cpu, cpu_smt_mask(core)) {
@@ -6367,9 +6367,9 @@ static inline void set_idle_cores(int cpu, int val)
 {
 }
 
-static inline bool test_idle_cores(int cpu, bool def)
+static inline bool test_idle_cores(int cpu)
 {
-	return def;
+	return false;
 }
 
 static inline int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
@@ -6608,7 +6608,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 		return target;
 
 	if (sched_smt_active()) {
-		has_idle_core = test_idle_cores(target, false);
+		has_idle_core = test_idle_cores(target);
 
 		if (!has_idle_core && cpus_share_cache(prev, target)) {
 			i = select_idle_smt(p, prev);

[PATCH v4 5/5] sched/fair: Cleanup for SIS_PROP

[Abel Wu]

The sched-domain of this cpu is only used for some heuristics when
SIS_PROP is enabled, and it should be irrelevant whether the local
sd_llc is valid or not, since all we care about is target sd_llc
if !SIS_PROP.

Access the local domain only when there is a need.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Acked-by: Mel Gorman <mgorman@suse.de>
---
 kernel/sched/fair.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 23b020c3d3a0..7bad641faef9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6396,19 +6396,19 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 	struct sched_domain_shared *sd_share;
 	struct rq *this_rq = this_rq();
 	int this = smp_processor_id();
-	struct sched_domain *this_sd;
+	struct sched_domain *this_sd = NULL;
 	u64 time = 0;
 
-	this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
-	if (!this_sd)
-		return -1;
-
 	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
 
 	if (sched_feat(SIS_PROP) && !has_idle_core) {
 		u64 avg_cost, avg_idle, span_avg;
 		unsigned long now = jiffies;
 
+		this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
+		if (!this_sd)
+			return -1;
+
 		/*
 		 * If we're busy, the assumption that the last idle period
 		 * predicts the future is flawed; age away the remaining
@@ -6462,7 +6462,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 	if (has_idle_core)
 		set_idle_cores(target, false);
 
-	if (sched_feat(SIS_PROP) && !has_idle_core) {
+	if (sched_feat(SIS_PROP) && this_sd && !has_idle_core) {
 		time = cpu_clock(this) - time;
 
 		/*
-- 
2.37.3

[tip: sched/core] sched/fair: Cleanup for SIS_PROP

[tip-bot2 for Abel Wu]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     96c1c0cfe493a7ed549169a6f044bbb83e490fb5
Gitweb:        https://git.kernel.org/tip/96c1c0cfe493a7ed549169a6f044bbb83e490fb5
Author:        Abel Wu <wuyun.abel@bytedance.com>
AuthorDate:    Wed, 07 Sep 2022 19:20:00 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 07 Sep 2022 21:53:47 +02:00

sched/fair: Cleanup for SIS_PROP

The sched-domain of this cpu is only used for some heuristics when
SIS_PROP is enabled, and it should be irrelevant whether the local
sd_llc is valid or not, since all we care about is target sd_llc
if !SIS_PROP.

Access the local domain only when there is a need.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20220907112000.1854-6-wuyun.abel@bytedance.com
---
 kernel/sched/fair.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 23b020c..7bad641 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6396,19 +6396,19 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool 
 	struct sched_domain_shared *sd_share;
 	struct rq *this_rq = this_rq();
 	int this = smp_processor_id();
-	struct sched_domain *this_sd;
+	struct sched_domain *this_sd = NULL;
 	u64 time = 0;
 
-	this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
-	if (!this_sd)
-		return -1;
-
 	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
 
 	if (sched_feat(SIS_PROP) && !has_idle_core) {
 		u64 avg_cost, avg_idle, span_avg;
 		unsigned long now = jiffies;
 
+		this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
+		if (!this_sd)
+			return -1;
+
 		/*
 		 * If we're busy, the assumption that the last idle period
 		 * predicts the future is flawed; age away the remaining
@@ -6462,7 +6462,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool 
 	if (has_idle_core)
 		set_idle_cores(target, false);
 
-	if (sched_feat(SIS_PROP) && !has_idle_core) {
+	if (sched_feat(SIS_PROP) && this_sd && !has_idle_core) {
 		time = cpu_clock(this) - time;
 
 		/*