[PATCH v5 0/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[PATCH v5 0/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[Yicong Yang]

This is the follow-up work to support cluster scheduler. Previously
we have added cluster level in the scheduler for both ARM64[1] and
X86[2] to support load balance between clusters to bring more memory
bandwidth and decrease cache contention. This patchset, on the other
hand, takes care of wake-up path by giving CPUs within the same cluster
a try before scanning the whole LLC to benefit those tasks communicating
with each other.

[1] 778c558f49a2 ("sched: Add cluster scheduler level in core and related Kconfig for ARM64")
[2] 66558b730f25 ("sched: Add cluster scheduler level for x86")

Change since v4:
- rename cpus_share_resources to cpus_share_lowest_cache to be more informative, per Tim
- return -1 when nr==0 in scan_cluster(), per Abel
Thanks!
Link: https://lore.kernel.org/lkml/20220609120622.47724-1-yangyicong@hisilicon.com/

Change since v3:
- fix compile error when !CONFIG_SCHED_CLUSTER, reported by lkp test.
Link: https://lore.kernel.org/lkml/20220608095758.60504-1-yangyicong@hisilicon.com/

Change since v2:
- leverage SIS_PROP to suspend redundant scanning when LLC is overloaded
- remove the ping-pong suppression
- address the comment from Tim, thanks.
Link: https://lore.kernel.org/lkml/20220126080947.4529-1-yangyicong@hisilicon.com/

Change since v1:
- regain the performance data based on v5.17-rc1
- rename cpus_share_cluster to cpus_share_resources per Vincent and Gautham, thanks!
Link: https://lore.kernel.org/lkml/20211215041149.73171-1-yangyicong@hisilicon.com/

Barry Song (2):
  sched: Add per_cpu cluster domain info and cpus_share_lowest_cache API
  sched/fair: Scan cluster before scanning LLC in wake-up path

 include/linux/sched/sd_flags.h |  7 ++++++
 include/linux/sched/topology.h |  8 ++++++-
 kernel/sched/core.c            | 12 ++++++++++
 kernel/sched/fair.c            | 44 +++++++++++++++++++++++++++++++---
 kernel/sched/sched.h           |  2 ++
 kernel/sched/topology.c        | 15 ++++++++++++
 6 files changed, 84 insertions(+), 4 deletions(-)

-- 
2.24.0

[PATCH v5 0/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[Yicong Yang]

This is the follow-up work to support cluster scheduler. Previously
we have added cluster level in the scheduler for both ARM64[1] and
X86[2] to support load balance between clusters to bring more memory
bandwidth and decrease cache contention. This patchset, on the other
hand, takes care of wake-up path by giving CPUs within the same cluster
a try before scanning the whole LLC to benefit those tasks communicating
with each other.

[1] 778c558f49a2 ("sched: Add cluster scheduler level in core and related Kconfig for ARM64")
[2] 66558b730f25 ("sched: Add cluster scheduler level for x86")

Change since v4:
- rename cpus_share_resources to cpus_share_lowest_cache to be more informative, per Tim
- return -1 when nr==0 in scan_cluster(), per Abel
Thanks!
Link: https://lore.kernel.org/lkml/20220609120622.47724-1-yangyicong@hisilicon.com/

Change since v3:
- fix compile error when !CONFIG_SCHED_CLUSTER, reported by lkp test.
Link: https://lore.kernel.org/lkml/20220608095758.60504-1-yangyicong@hisilicon.com/

Change since v2:
- leverage SIS_PROP to suspend redundant scanning when LLC is overloaded
- remove the ping-pong suppression
- address the comment from Tim, thanks.
Link: https://lore.kernel.org/lkml/20220126080947.4529-1-yangyicong@hisilicon.com/

Change since v1:
- regain the performance data based on v5.17-rc1
- rename cpus_share_cluster to cpus_share_resources per Vincent and Gautham, thanks!
Link: https://lore.kernel.org/lkml/20211215041149.73171-1-yangyicong@hisilicon.com/

Barry Song (2):
  sched: Add per_cpu cluster domain info and cpus_share_lowest_cache API
  sched/fair: Scan cluster before scanning LLC in wake-up path

 include/linux/sched/sd_flags.h |  7 ++++++
 include/linux/sched/topology.h |  8 ++++++-
 kernel/sched/core.c            | 12 ++++++++++
 kernel/sched/fair.c            | 44 +++++++++++++++++++++++++++++++---
 kernel/sched/sched.h           |  2 ++
 kernel/sched/topology.c        | 15 ++++++++++++
 6 files changed, 84 insertions(+), 4 deletions(-)

-- 
2.24.0


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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v5 1/2] sched: Add per_cpu cluster domain info and cpus_share_lowest_cache API

[Yicong Yang]

From: Barry Song <song.bao.hua@hisilicon.com>

Add per-cpu cluster domain info and cpus_share_lowest_cache() API.
This is the preparation for the optimization of select_idle_cpu()
on platforms with cluster scheduler level.

Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 include/linux/sched/sd_flags.h |  7 +++++++
 include/linux/sched/topology.h |  8 +++++++-
 kernel/sched/core.c            | 12 ++++++++++++
 kernel/sched/sched.h           |  2 ++
 kernel/sched/topology.c        | 15 +++++++++++++++
 5 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h
index 57bde66d95f7..42ed454e8b18 100644
--- a/include/linux/sched/sd_flags.h
+++ b/include/linux/sched/sd_flags.h
@@ -109,6 +109,13 @@ SD_FLAG(SD_ASYM_CPUCAPACITY_FULL, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS)
  */
 SD_FLAG(SD_SHARE_CPUCAPACITY, SDF_SHARED_CHILD | SDF_NEEDS_GROUPS)
 
+/*
+ * Domain members share CPU cluster (LLC tags or L2 cache)
+ *
+ * NEEDS_GROUPS: Clusters are shared between groups.
+ */
+SD_FLAG(SD_CLUSTER, SDF_NEEDS_GROUPS)
+
 /*
  * Domain members share CPU package resources (i.e. caches)
  *
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 816df6cc444e..c0d21667ddf3 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -45,7 +45,7 @@ static inline int cpu_smt_flags(void)
 #ifdef CONFIG_SCHED_CLUSTER
 static inline int cpu_cluster_flags(void)
 {
-	return SD_SHARE_PKG_RESOURCES;
+	return SD_CLUSTER | SD_SHARE_PKG_RESOURCES;
 }
 #endif
 
@@ -179,6 +179,7 @@ cpumask_var_t *alloc_sched_domains(unsigned int ndoms);
 void free_sched_domains(cpumask_var_t doms[], unsigned int ndoms);
 
 bool cpus_share_cache(int this_cpu, int that_cpu);
+bool cpus_share_lowest_cache(int this_cpu, int that_cpu);
 
 typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);
 typedef int (*sched_domain_flags_f)(void);
@@ -232,6 +233,11 @@ static inline bool cpus_share_cache(int this_cpu, int that_cpu)
 	return true;
 }
 
+static inline bool cpus_share_lowest_cache(int this_cpu, int that_cpu)
+{
+	return true;
+}
+
 #endif	/* !CONFIG_SMP */
 
 #if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d3e2c5a7c1b7..2e6816aeaa2b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3808,6 +3808,18 @@ bool cpus_share_cache(int this_cpu, int that_cpu)
 	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
 }
 
+/*
+ * Whether CPUs are share lowest cache, which means LLC on non-cluster
+ * machines and LLC tag or L2 on machines with clusters.
+ */
+bool cpus_share_lowest_cache(int this_cpu, int that_cpu)
+{
+	if (this_cpu == that_cpu)
+		return true;
+
+	return per_cpu(sd_lowest_cache_id, this_cpu) == per_cpu(sd_lowest_cache_id, that_cpu);
+}
+
 static inline bool ttwu_queue_cond(int cpu)
 {
 	/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 02c970501295..767e637ceb5a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1753,7 +1753,9 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DECLARE_PER_CPU(int, sd_llc_size);
 DECLARE_PER_CPU(int, sd_llc_id);
+DECLARE_PER_CPU(int, sd_lowest_cache_id);
 DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
+DECLARE_PER_CPU(struct sched_domain __rcu *, sd_cluster);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8739c2a5a54e..8ab27c0d6d1f 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -664,6 +664,8 @@ static void destroy_sched_domains(struct sched_domain *sd)
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DEFINE_PER_CPU(int, sd_llc_size);
 DEFINE_PER_CPU(int, sd_llc_id);
+DEFINE_PER_CPU(int, sd_lowest_cache_id);
+DEFINE_PER_CPU(struct sched_domain __rcu *, sd_cluster);
 DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
@@ -689,6 +691,18 @@ static void update_top_cache_domain(int cpu)
 	per_cpu(sd_llc_id, cpu) = id;
 	rcu_assign_pointer(per_cpu(sd_llc_shared, cpu), sds);
 
+	sd = lowest_flag_domain(cpu, SD_CLUSTER);
+	if (sd)
+		id = cpumask_first(sched_domain_span(sd));
+	rcu_assign_pointer(per_cpu(sd_cluster, cpu), sd);
+
+	/*
+	 * This assignment should be placed after the sd_llc_id as
+	 * we want this id equals to cluster id on cluster machines
+	 * but equals to LLC id on non-Cluster machines.
+	 */
+	per_cpu(sd_lowest_cache_id, cpu) = id;
+
 	sd = lowest_flag_domain(cpu, SD_NUMA);
 	rcu_assign_pointer(per_cpu(sd_numa, cpu), sd);
 
@@ -1532,6 +1546,7 @@ static struct cpumask		***sched_domains_numa_masks;
  */
 #define TOPOLOGY_SD_FLAGS		\
 	(SD_SHARE_CPUCAPACITY	|	\
+	 SD_CLUSTER		|	\
 	 SD_SHARE_PKG_RESOURCES |	\
 	 SD_NUMA		|	\
 	 SD_ASYM_PACKING)
-- 
2.24.0

[PATCH v5 1/2] sched: Add per_cpu cluster domain info and cpus_share_lowest_cache API

[Yicong Yang]

From: Barry Song <song.bao.hua@hisilicon.com>

Add per-cpu cluster domain info and cpus_share_lowest_cache() API.
This is the preparation for the optimization of select_idle_cpu()
on platforms with cluster scheduler level.

Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 include/linux/sched/sd_flags.h |  7 +++++++
 include/linux/sched/topology.h |  8 +++++++-
 kernel/sched/core.c            | 12 ++++++++++++
 kernel/sched/sched.h           |  2 ++
 kernel/sched/topology.c        | 15 +++++++++++++++
 5 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h
index 57bde66d95f7..42ed454e8b18 100644
--- a/include/linux/sched/sd_flags.h
+++ b/include/linux/sched/sd_flags.h
@@ -109,6 +109,13 @@ SD_FLAG(SD_ASYM_CPUCAPACITY_FULL, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS)
  */
 SD_FLAG(SD_SHARE_CPUCAPACITY, SDF_SHARED_CHILD | SDF_NEEDS_GROUPS)
 
+/*
+ * Domain members share CPU cluster (LLC tags or L2 cache)
+ *
+ * NEEDS_GROUPS: Clusters are shared between groups.
+ */
+SD_FLAG(SD_CLUSTER, SDF_NEEDS_GROUPS)
+
 /*
  * Domain members share CPU package resources (i.e. caches)
  *
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 816df6cc444e..c0d21667ddf3 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -45,7 +45,7 @@ static inline int cpu_smt_flags(void)
 #ifdef CONFIG_SCHED_CLUSTER
 static inline int cpu_cluster_flags(void)
 {
-	return SD_SHARE_PKG_RESOURCES;
+	return SD_CLUSTER | SD_SHARE_PKG_RESOURCES;
 }
 #endif
 
@@ -179,6 +179,7 @@ cpumask_var_t *alloc_sched_domains(unsigned int ndoms);
 void free_sched_domains(cpumask_var_t doms[], unsigned int ndoms);
 
 bool cpus_share_cache(int this_cpu, int that_cpu);
+bool cpus_share_lowest_cache(int this_cpu, int that_cpu);
 
 typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);
 typedef int (*sched_domain_flags_f)(void);
@@ -232,6 +233,11 @@ static inline bool cpus_share_cache(int this_cpu, int that_cpu)
 	return true;
 }
 
+static inline bool cpus_share_lowest_cache(int this_cpu, int that_cpu)
+{
+	return true;
+}
+
 #endif	/* !CONFIG_SMP */
 
 #if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d3e2c5a7c1b7..2e6816aeaa2b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3808,6 +3808,18 @@ bool cpus_share_cache(int this_cpu, int that_cpu)
 	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
 }
 
+/*
+ * Whether CPUs are share lowest cache, which means LLC on non-cluster
+ * machines and LLC tag or L2 on machines with clusters.
+ */
+bool cpus_share_lowest_cache(int this_cpu, int that_cpu)
+{
+	if (this_cpu == that_cpu)
+		return true;
+
+	return per_cpu(sd_lowest_cache_id, this_cpu) == per_cpu(sd_lowest_cache_id, that_cpu);
+}
+
 static inline bool ttwu_queue_cond(int cpu)
 {
 	/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 02c970501295..767e637ceb5a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1753,7 +1753,9 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DECLARE_PER_CPU(int, sd_llc_size);
 DECLARE_PER_CPU(int, sd_llc_id);
+DECLARE_PER_CPU(int, sd_lowest_cache_id);
 DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
+DECLARE_PER_CPU(struct sched_domain __rcu *, sd_cluster);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8739c2a5a54e..8ab27c0d6d1f 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -664,6 +664,8 @@ static void destroy_sched_domains(struct sched_domain *sd)
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DEFINE_PER_CPU(int, sd_llc_size);
 DEFINE_PER_CPU(int, sd_llc_id);
+DEFINE_PER_CPU(int, sd_lowest_cache_id);
+DEFINE_PER_CPU(struct sched_domain __rcu *, sd_cluster);
 DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
@@ -689,6 +691,18 @@ static void update_top_cache_domain(int cpu)
 	per_cpu(sd_llc_id, cpu) = id;
 	rcu_assign_pointer(per_cpu(sd_llc_shared, cpu), sds);
 
+	sd = lowest_flag_domain(cpu, SD_CLUSTER);
+	if (sd)
+		id = cpumask_first(sched_domain_span(sd));
+	rcu_assign_pointer(per_cpu(sd_cluster, cpu), sd);
+
+	/*
+	 * This assignment should be placed after the sd_llc_id as
+	 * we want this id equals to cluster id on cluster machines
+	 * but equals to LLC id on non-Cluster machines.
+	 */
+	per_cpu(sd_lowest_cache_id, cpu) = id;
+
 	sd = lowest_flag_domain(cpu, SD_NUMA);
 	rcu_assign_pointer(per_cpu(sd_numa, cpu), sd);
 
@@ -1532,6 +1546,7 @@ static struct cpumask		***sched_domains_numa_masks;
  */
 #define TOPOLOGY_SD_FLAGS		\
 	(SD_SHARE_CPUCAPACITY	|	\
+	 SD_CLUSTER		|	\
 	 SD_SHARE_PKG_RESOURCES |	\
 	 SD_NUMA		|	\
 	 SD_ASYM_PACKING)
-- 
2.24.0


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[PATCH v5 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[Yicong Yang]

From: Barry Song <song.bao.hua@hisilicon.com>

For platforms having clusters like Kunpeng920, CPUs within the same cluster
have lower latency when synchronizing and accessing shared resources like
cache. Thus, this patch tries to find an idle cpu within the cluster of the
target CPU before scanning the whole LLC to gain lower latency.

Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so this patch
doesn't consider SMT for this moment.

Testing has been done on Kunpeng920 by pinning tasks to one numa and two
numa. On Kunpeng920, Each numa has 8 clusters and each cluster has 4 CPUs.

With this patch, We noticed enhancement on tbench within one numa or cross
two numa.

On numa 0:
                           tip/core                 patched
Hmean     1        345.89 (   0.00%)      393.96 *  13.90%*
Hmean     2        697.77 (   0.00%)      786.04 *  12.65%*
Hmean     4       1392.51 (   0.00%)     1570.26 *  12.76%*
Hmean     8       2800.61 (   0.00%)     3083.98 *  10.12%*
Hmean     16      5514.27 (   0.00%)     6116.00 *  10.91%*
Hmean     32     10869.81 (   0.00%)    10782.98 *  -0.80%*
Hmean     64      8315.22 (   0.00%)     8519.84 *   2.46%*
Hmean     128     6324.47 (   0.00%)     7159.35 *  13.20%*

On numa 0-1:
                           tip/core                 patched
Hmean     1        348.68 (   0.00%)      387.91 *  11.25%*
Hmean     2        693.57 (   0.00%)      774.91 *  11.73%*
Hmean     4       1369.26 (   0.00%)     1475.48 *   7.76%*
Hmean     8       2772.99 (   0.00%)     2984.61 *   7.63%*
Hmean     16      4825.83 (   0.00%)     5873.13 *  21.70%*
Hmean     32     10250.32 (   0.00%)    11688.06 *  14.03%*
Hmean     64     16309.51 (   0.00%)    19889.48 *  21.95%*
Hmean     128    13022.32 (   0.00%)    16005.64 *  22.91%*
Hmean     256    11335.79 (   0.00%)    13821.74 *  21.93%*

Tested-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 44 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f80ae86bb404..dff5dec0d792 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6323,6 +6323,40 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd
 
 #endif /* CONFIG_SCHED_SMT */
 
+#ifdef CONFIG_SCHED_CLUSTER
+/*
+ * Scan the cluster domain for idle CPUs and clear cluster cpumask after scanning
+ */
+static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
+			       int target, int *nr)
+{
+	struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target));
+	int cpu, idle_cpu;
+
+	/* TODO: Support SMT system with cluster topology */
+	if (!sched_smt_active() && sd) {
+		for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
+			if (!--*nr)
+				return -1;
+
+			idle_cpu = __select_idle_cpu(cpu, p);
+			if ((unsigned int)idle_cpu < nr_cpumask_bits)
+				return idle_cpu;
+		}
+
+		cpumask_andnot(cpus, cpus, sched_domain_span(sd));
+	}
+
+	return -1;
+}
+#else
+static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
+			       int target, int *nr)
+{
+	return -1;
+}
+#endif
+
 /*
  * Scan the LLC domain for idle CPUs; this is dynamically regulated by
  * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
@@ -6383,6 +6417,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 		}
 	}
 
+	idle_cpu = scan_cluster(p, cpus, target, &nr);
+	if ((unsigned int)idle_cpu < nr_cpumask_bits)
+		return idle_cpu;
+
 	for_each_cpu_wrap(cpu, cpus, target + 1) {
 		if (has_idle_core) {
 			i = select_idle_core(p, cpu, cpus, &idle_cpu);
@@ -6390,7 +6428,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 				return i;
 
 		} else {
-			if (!--nr)
+			if (--nr <= 0)
 				return -1;
 			idle_cpu = __select_idle_cpu(cpu, p);
 			if ((unsigned int)idle_cpu < nr_cpumask_bits)
@@ -6489,7 +6527,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	/*
 	 * If the previous CPU is cache affine and idle, don't be stupid:
 	 */
-	if (prev != target && cpus_share_cache(prev, target) &&
+	if (prev != target && cpus_share_lowest_cache(prev, target) &&
 	    (available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
 	    asym_fits_capacity(task_util, prev))
 		return prev;
@@ -6515,7 +6553,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	p->recent_used_cpu = prev;
 	if (recent_used_cpu != prev &&
 	    recent_used_cpu != target &&
-	    cpus_share_cache(recent_used_cpu, target) &&
+	    cpus_share_lowest_cache(recent_used_cpu, target) &&
 	    (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
 	    cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) &&
 	    asym_fits_capacity(task_util, recent_used_cpu)) {
-- 
2.24.0

[PATCH v5 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[Yicong Yang]

From: Barry Song <song.bao.hua@hisilicon.com>

For platforms having clusters like Kunpeng920, CPUs within the same cluster
have lower latency when synchronizing and accessing shared resources like
cache. Thus, this patch tries to find an idle cpu within the cluster of the
target CPU before scanning the whole LLC to gain lower latency.

Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so this patch
doesn't consider SMT for this moment.

Testing has been done on Kunpeng920 by pinning tasks to one numa and two
numa. On Kunpeng920, Each numa has 8 clusters and each cluster has 4 CPUs.

With this patch, We noticed enhancement on tbench within one numa or cross
two numa.

On numa 0:
                           tip/core                 patched
Hmean     1        345.89 (   0.00%)      393.96 *  13.90%*
Hmean     2        697.77 (   0.00%)      786.04 *  12.65%*
Hmean     4       1392.51 (   0.00%)     1570.26 *  12.76%*
Hmean     8       2800.61 (   0.00%)     3083.98 *  10.12%*
Hmean     16      5514.27 (   0.00%)     6116.00 *  10.91%*
Hmean     32     10869.81 (   0.00%)    10782.98 *  -0.80%*
Hmean     64      8315.22 (   0.00%)     8519.84 *   2.46%*
Hmean     128     6324.47 (   0.00%)     7159.35 *  13.20%*

On numa 0-1:
                           tip/core                 patched
Hmean     1        348.68 (   0.00%)      387.91 *  11.25%*
Hmean     2        693.57 (   0.00%)      774.91 *  11.73%*
Hmean     4       1369.26 (   0.00%)     1475.48 *   7.76%*
Hmean     8       2772.99 (   0.00%)     2984.61 *   7.63%*
Hmean     16      4825.83 (   0.00%)     5873.13 *  21.70%*
Hmean     32     10250.32 (   0.00%)    11688.06 *  14.03%*
Hmean     64     16309.51 (   0.00%)    19889.48 *  21.95%*
Hmean     128    13022.32 (   0.00%)    16005.64 *  22.91%*
Hmean     256    11335.79 (   0.00%)    13821.74 *  21.93%*

Tested-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 44 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f80ae86bb404..dff5dec0d792 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6323,6 +6323,40 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd
 
 #endif /* CONFIG_SCHED_SMT */
 
+#ifdef CONFIG_SCHED_CLUSTER
+/*
+ * Scan the cluster domain for idle CPUs and clear cluster cpumask after scanning
+ */
+static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
+			       int target, int *nr)
+{
+	struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target));
+	int cpu, idle_cpu;
+
+	/* TODO: Support SMT system with cluster topology */
+	if (!sched_smt_active() && sd) {
+		for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
+			if (!--*nr)
+				return -1;
+
+			idle_cpu = __select_idle_cpu(cpu, p);
+			if ((unsigned int)idle_cpu < nr_cpumask_bits)
+				return idle_cpu;
+		}
+
+		cpumask_andnot(cpus, cpus, sched_domain_span(sd));
+	}
+
+	return -1;
+}
+#else
+static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
+			       int target, int *nr)
+{
+	return -1;
+}
+#endif
+
 /*
  * Scan the LLC domain for idle CPUs; this is dynamically regulated by
  * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
@@ -6383,6 +6417,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 		}
 	}
 
+	idle_cpu = scan_cluster(p, cpus, target, &nr);
+	if ((unsigned int)idle_cpu < nr_cpumask_bits)
+		return idle_cpu;
+
 	for_each_cpu_wrap(cpu, cpus, target + 1) {
 		if (has_idle_core) {
 			i = select_idle_core(p, cpu, cpus, &idle_cpu);
@@ -6390,7 +6428,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 				return i;
 
 		} else {
-			if (!--nr)
+			if (--nr <= 0)
 				return -1;
 			idle_cpu = __select_idle_cpu(cpu, p);
 			if ((unsigned int)idle_cpu < nr_cpumask_bits)
@@ -6489,7 +6527,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	/*
 	 * If the previous CPU is cache affine and idle, don't be stupid:
 	 */
-	if (prev != target && cpus_share_cache(prev, target) &&
+	if (prev != target && cpus_share_lowest_cache(prev, target) &&
 	    (available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
 	    asym_fits_capacity(task_util, prev))
 		return prev;
@@ -6515,7 +6553,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	p->recent_used_cpu = prev;
 	if (recent_used_cpu != prev &&
 	    recent_used_cpu != target &&
-	    cpus_share_cache(recent_used_cpu, target) &&
+	    cpus_share_lowest_cache(recent_used_cpu, target) &&
 	    (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
 	    cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) &&
 	    asym_fits_capacity(task_util, recent_used_cpu)) {
-- 
2.24.0


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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH v5 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[Yicong Yang]

Hi,

a friendly ping..

On 2022/6/30 14:55, Yicong Yang wrote:
> From: Barry Song <song.bao.hua@hisilicon.com>
> 
> For platforms having clusters like Kunpeng920, CPUs within the same cluster
> have lower latency when synchronizing and accessing shared resources like
> cache. Thus, this patch tries to find an idle cpu within the cluster of the
> target CPU before scanning the whole LLC to gain lower latency.
> 
> Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so this patch
> doesn't consider SMT for this moment.
> 
> Testing has been done on Kunpeng920 by pinning tasks to one numa and two
> numa. On Kunpeng920, Each numa has 8 clusters and each cluster has 4 CPUs.
> 
> With this patch, We noticed enhancement on tbench within one numa or cross
> two numa.
> 
> On numa 0:
>                            tip/core                 patched
> Hmean     1        345.89 (   0.00%)      393.96 *  13.90%*
> Hmean     2        697.77 (   0.00%)      786.04 *  12.65%*
> Hmean     4       1392.51 (   0.00%)     1570.26 *  12.76%*
> Hmean     8       2800.61 (   0.00%)     3083.98 *  10.12%*
> Hmean     16      5514.27 (   0.00%)     6116.00 *  10.91%*
> Hmean     32     10869.81 (   0.00%)    10782.98 *  -0.80%*
> Hmean     64      8315.22 (   0.00%)     8519.84 *   2.46%*
> Hmean     128     6324.47 (   0.00%)     7159.35 *  13.20%*
> 
> On numa 0-1:
>                            tip/core                 patched
> Hmean     1        348.68 (   0.00%)      387.91 *  11.25%*
> Hmean     2        693.57 (   0.00%)      774.91 *  11.73%*
> Hmean     4       1369.26 (   0.00%)     1475.48 *   7.76%*
> Hmean     8       2772.99 (   0.00%)     2984.61 *   7.63%*
> Hmean     16      4825.83 (   0.00%)     5873.13 *  21.70%*
> Hmean     32     10250.32 (   0.00%)    11688.06 *  14.03%*
> Hmean     64     16309.51 (   0.00%)    19889.48 *  21.95%*
> Hmean     128    13022.32 (   0.00%)    16005.64 *  22.91%*
> Hmean     256    11335.79 (   0.00%)    13821.74 *  21.93%*
> 
> Tested-by: Yicong Yang <yangyicong@hisilicon.com>
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
> Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
> ---
>  kernel/sched/fair.c | 44 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 41 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f80ae86bb404..dff5dec0d792 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6323,6 +6323,40 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd
>  
>  #endif /* CONFIG_SCHED_SMT */
>  
> +#ifdef CONFIG_SCHED_CLUSTER
> +/*
> + * Scan the cluster domain for idle CPUs and clear cluster cpumask after scanning
> + */
> +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
> +			       int target, int *nr)
> +{
> +	struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target));
> +	int cpu, idle_cpu;
> +
> +	/* TODO: Support SMT system with cluster topology */
> +	if (!sched_smt_active() && sd) {
> +		for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
> +			if (!--*nr)
> +				return -1;
> +
> +			idle_cpu = __select_idle_cpu(cpu, p);
> +			if ((unsigned int)idle_cpu < nr_cpumask_bits)
> +				return idle_cpu;
> +		}
> +
> +		cpumask_andnot(cpus, cpus, sched_domain_span(sd));
> +	}
> +
> +	return -1;
> +}
> +#else
> +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
> +			       int target, int *nr)
> +{
> +	return -1;
> +}
> +#endif
> +
>  /*
>   * Scan the LLC domain for idle CPUs; this is dynamically regulated by
>   * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
> @@ -6383,6 +6417,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>  		}
>  	}
>  
> +	idle_cpu = scan_cluster(p, cpus, target, &nr);
> +	if ((unsigned int)idle_cpu < nr_cpumask_bits)
> +		return idle_cpu;
> +
>  	for_each_cpu_wrap(cpu, cpus, target + 1) {
>  		if (has_idle_core) {
>  			i = select_idle_core(p, cpu, cpus, &idle_cpu);
> @@ -6390,7 +6428,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>  				return i;
>  
>  		} else {
> -			if (!--nr)
> +			if (--nr <= 0)
>  				return -1;
>  			idle_cpu = __select_idle_cpu(cpu, p);
>  			if ((unsigned int)idle_cpu < nr_cpumask_bits)
> @@ -6489,7 +6527,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>  	/*
>  	 * If the previous CPU is cache affine and idle, don't be stupid:
>  	 */
> -	if (prev != target && cpus_share_cache(prev, target) &&
> +	if (prev != target && cpus_share_lowest_cache(prev, target) &&
>  	    (available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
>  	    asym_fits_capacity(task_util, prev))
>  		return prev;
> @@ -6515,7 +6553,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>  	p->recent_used_cpu = prev;
>  	if (recent_used_cpu != prev &&
>  	    recent_used_cpu != target &&
> -	    cpus_share_cache(recent_used_cpu, target) &&
> +	    cpus_share_lowest_cache(recent_used_cpu, target) &&
>  	    (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
>  	    cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) &&
>  	    asym_fits_capacity(task_util, recent_used_cpu)) {
> 

Re: [PATCH v5 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[Yicong Yang]

Hi,

a friendly ping..

On 2022/6/30 14:55, Yicong Yang wrote:
> From: Barry Song <song.bao.hua@hisilicon.com>
> 
> For platforms having clusters like Kunpeng920, CPUs within the same cluster
> have lower latency when synchronizing and accessing shared resources like
> cache. Thus, this patch tries to find an idle cpu within the cluster of the
> target CPU before scanning the whole LLC to gain lower latency.
> 
> Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so this patch
> doesn't consider SMT for this moment.
> 
> Testing has been done on Kunpeng920 by pinning tasks to one numa and two
> numa. On Kunpeng920, Each numa has 8 clusters and each cluster has 4 CPUs.
> 
> With this patch, We noticed enhancement on tbench within one numa or cross
> two numa.
> 
> On numa 0:
>                            tip/core                 patched
> Hmean     1        345.89 (   0.00%)      393.96 *  13.90%*
> Hmean     2        697.77 (   0.00%)      786.04 *  12.65%*
> Hmean     4       1392.51 (   0.00%)     1570.26 *  12.76%*
> Hmean     8       2800.61 (   0.00%)     3083.98 *  10.12%*
> Hmean     16      5514.27 (   0.00%)     6116.00 *  10.91%*
> Hmean     32     10869.81 (   0.00%)    10782.98 *  -0.80%*
> Hmean     64      8315.22 (   0.00%)     8519.84 *   2.46%*
> Hmean     128     6324.47 (   0.00%)     7159.35 *  13.20%*
> 
> On numa 0-1:
>                            tip/core                 patched
> Hmean     1        348.68 (   0.00%)      387.91 *  11.25%*
> Hmean     2        693.57 (   0.00%)      774.91 *  11.73%*
> Hmean     4       1369.26 (   0.00%)     1475.48 *   7.76%*
> Hmean     8       2772.99 (   0.00%)     2984.61 *   7.63%*
> Hmean     16      4825.83 (   0.00%)     5873.13 *  21.70%*
> Hmean     32     10250.32 (   0.00%)    11688.06 *  14.03%*
> Hmean     64     16309.51 (   0.00%)    19889.48 *  21.95%*
> Hmean     128    13022.32 (   0.00%)    16005.64 *  22.91%*
> Hmean     256    11335.79 (   0.00%)    13821.74 *  21.93%*
> 
> Tested-by: Yicong Yang <yangyicong@hisilicon.com>
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
> Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
> ---
>  kernel/sched/fair.c | 44 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 41 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f80ae86bb404..dff5dec0d792 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6323,6 +6323,40 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd
>  
>  #endif /* CONFIG_SCHED_SMT */
>  
> +#ifdef CONFIG_SCHED_CLUSTER
> +/*
> + * Scan the cluster domain for idle CPUs and clear cluster cpumask after scanning
> + */
> +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
> +			       int target, int *nr)
> +{
> +	struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target));
> +	int cpu, idle_cpu;
> +
> +	/* TODO: Support SMT system with cluster topology */
> +	if (!sched_smt_active() && sd) {
> +		for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
> +			if (!--*nr)
> +				return -1;
> +
> +			idle_cpu = __select_idle_cpu(cpu, p);
> +			if ((unsigned int)idle_cpu < nr_cpumask_bits)
> +				return idle_cpu;
> +		}
> +
> +		cpumask_andnot(cpus, cpus, sched_domain_span(sd));
> +	}
> +
> +	return -1;
> +}
> +#else
> +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
> +			       int target, int *nr)
> +{
> +	return -1;
> +}
> +#endif
> +
>  /*
>   * Scan the LLC domain for idle CPUs; this is dynamically regulated by
>   * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
> @@ -6383,6 +6417,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>  		}
>  	}
>  
> +	idle_cpu = scan_cluster(p, cpus, target, &nr);
> +	if ((unsigned int)idle_cpu < nr_cpumask_bits)
> +		return idle_cpu;
> +
>  	for_each_cpu_wrap(cpu, cpus, target + 1) {
>  		if (has_idle_core) {
>  			i = select_idle_core(p, cpu, cpus, &idle_cpu);
> @@ -6390,7 +6428,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>  				return i;
>  
>  		} else {
> -			if (!--nr)
> +			if (--nr <= 0)
>  				return -1;
>  			idle_cpu = __select_idle_cpu(cpu, p);
>  			if ((unsigned int)idle_cpu < nr_cpumask_bits)
> @@ -6489,7 +6527,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>  	/*
>  	 * If the previous CPU is cache affine and idle, don't be stupid:
>  	 */
> -	if (prev != target && cpus_share_cache(prev, target) &&
> +	if (prev != target && cpus_share_lowest_cache(prev, target) &&
>  	    (available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
>  	    asym_fits_capacity(task_util, prev))
>  		return prev;
> @@ -6515,7 +6553,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>  	p->recent_used_cpu = prev;
>  	if (recent_used_cpu != prev &&
>  	    recent_used_cpu != target &&
> -	    cpus_share_cache(recent_used_cpu, target) &&
> +	    cpus_share_lowest_cache(recent_used_cpu, target) &&
>  	    (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
>  	    cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) &&
>  	    asym_fits_capacity(task_util, recent_used_cpu)) {
> 

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