[RFC PATCH v5 2/4] scheduler: add scheduler level for clusters

Barry Song
2021-03-19T04:24:20Z

ARM64 chip Kunpeng 920 has 6 or 8 clusters in each NUMA node, and each
cluster has 4 cpus. All clusters share L3 cache data, but each cluster
has local L3 tag. On the other hand, each clusters will share some
internal system bus. This means cache coherence overhead inside one
cluster is much less than the overhead across clusters.

This patch adds the sched_domain for clusters. On kunpeng 920, without
this patch, domain0 of cpu0 would be MC with cpu0~cpu23 with ; with this
patch, MC becomes domain1, a new domain0 "CLS" including cpu0-cpu3.

This will help spread unrelated tasks among clusters, thus decrease the
contention and improve the throughput, for example, stream benchmark can
improve 20%+ while parallelism is 6 and improve around 5% while paralle-
lism is 12:

(1) -P <parallelism> 6
$ numactl -N 0 /usr/lib/lmbench/bin/stream -P 6 -M 1024M -N 5

w/o patch:
STREAM copy latency: 2.46 nanoseconds
STREAM copy bandwidth: 39096.28 MB/sec
STREAM scale latency: 2.46 nanoseconds
STREAM scale bandwidth: 38970.26 MB/sec
STREAM add latency: 4.45 nanoseconds
STREAM add bandwidth: 32332.04 MB/sec
STREAM triad latency: 4.07 nanoseconds
STREAM triad bandwidth: 35387.69 MB/sec

w/ patch:
STREAM copy latency: 2.02 nanoseconds
STREAM copy bandwidth: 47604.47 MB/sec +21.7%
STREAM scale latency: 2.04 nanoseconds
STREAM scale bandwidth: 47066.84 MB/sec +20.8%
STREAM add latency: 3.35 nanoseconds
STREAM add bandwidth: 42942.15 MB/sec +32.8%
STREAM triad latency: 3.16 nanoseconds
STREAM triad bandwidth: 45619.18 MB/sec +28.9%

On the other hand,stream result could change significantly during different
tests without the patch, eg:
a.
STREAM copy latency: 2.16 nanoseconds
STREAM copy bandwidth: 44448.45 MB/sec
STREAM scale latency: 2.17 nanoseconds
STREAM scale bandwidth: 44320.77 MB/sec
STREAM add latency: 3.77 nanoseconds
STREAM add bandwidth: 38230.54 MB/sec
STREAM triad latency: 3.88 nanoseconds
STREAM triad bandwidth: 37072.10 MB/sec

b.
STREAM copy latency: 2.16 nanoseconds
STREAM copy bandwidth: 44403.22 MB/sec
STREAM scale latency: 2.39 nanoseconds
STREAM scale bandwidth: 40173.69 MB/sec
STREAM add latency: 3.77 nanoseconds
STREAM add bandwidth: 38232.56 MB/sec
STREAM triad latency: 3.38 nanoseconds
STREAM triad bandwidth: 42592.04 MB/sec

Obviously it is because the 6 threads are put randomly in 6 cores. Sometimes
they are packed in clusters, sometimes they are spread widely.

(2) -P <parallelism> 12
$ numactl -N 0 /usr/lib/lmbench/bin/stream -P 12 -M 1024M -N 5

w/o patch:
STREAM copy latency: 3.37 nanoseconds
STREAM copy bandwidth: 57008.80 MB/sec
STREAM scale latency: 3.38 nanoseconds
STREAM scale bandwidth: 56848.47 MB/sec
STREAM add latency: 5.50 nanoseconds
STREAM add bandwidth: 52398.62 MB/sec
STREAM triad latency: 5.09 nanoseconds
STREAM triad bandwidth: 56591.60 MB/sec

w/ patch:
STREAM copy latency: 3.24 nanoseconds
STREAM copy bandwidth: 59338.60 MB/sec +4.1%
STREAM scale latency: 3.25 nanoseconds
STREAM scale bandwidth: 58993.23 MB/sec +3.7%
STREAM add latency: 5.19 nanoseconds
STREAM add bandwidth: 55517.45 MB/sec +5.9%
STREAM triad latency: 4.86 nanoseconds
STREAM triad bandwidth: 59245.34 MB/sec +4.7%

To evaluate the performance impact to related tasks talking with each
other, we run the below hackbench with different -g parameter from 2
to 14, for each different g, we run the command 10 times and get the
average time:
$ numactl -N 0 hackbench -p -T -l 20000 -g $1

hackbench will report the time which is needed to complete a certain number
of messages transmissions between a certain number of tasks, for example:
$ numactl -N 0 hackbench -p -T -l 20000 -g 10
Running in threaded mode with 10 groups using 40 file descriptors each
(== 400 tasks)
Each sender will pass 20000 messages of 100 bytes

The below is the result of hackbench w/ and w/o the patch:
g= 2 4 6 8 10 12 14
w/o: 1.8151 3.8499 5.5142 7.2491 9.0340 10.7345 12.0929
w/ : 1.8396 3.8250 5.4780 7.3442 9.0172 10.5950 11.9113

Obviously this patch doesn't impact hackbench too much.

Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
---
arch/arm64/Kconfig | 7 +++++++
include/linux/sched/cluster.h | 19 +++++++++++++++++++
include/linux/sched/topology.h | 7 +++++++
include/linux/topology.h | 7 +++++++
kernel/sched/core.c | 20 ++++++++++++++++++++
kernel/sched/fair.c | 4 ++++
kernel/sched/sched.h | 1 +
kernel/sched/topology.c | 5 +++++
8 files changed, 70 insertions(+)
create mode 100644 include/linux/sched/cluster.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1f212b4..9432a30 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -977,6 +977,13 @@ config SCHED_MC
making when dealing with multi-core CPU chips at a cost of slightly
increased overhead in some places. If unsure say N here.

+config SCHED_CLUSTER
+ bool "Cluster scheduler support"
+ help
+ Cluster scheduler support improves the CPU scheduler's decision
+ making when dealing with machines that have clusters(sharing internal
+ bus or sharing LLC cache tag). If unsure say N here.
+
config SCHED_SMT
bool "SMT scheduler support"
help
diff --git a/include/linux/sched/cluster.h b/include/linux/sched/cluster.h
new file mode 100644
index 0000000..ea6c475
--- /dev/null
+++ b/include/linux/sched/cluster.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_SCHED_CLUSTER_H
+#define _LINUX_SCHED_CLUSTER_H
+
+#include <linux/static_key.h>
+
+#ifdef CONFIG_SCHED_CLUSTER
+extern struct static_key_false sched_cluster_present;
+
+static __always_inline bool sched_cluster_active(void)
+{
+ return static_branch_likely(&sched_cluster_present);
+}
+#else
+static inline bool sched_cluster_active(void) { return false; }
+
+#endif
+
+#endif
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 8f0f778..2f9166f 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -42,6 +42,13 @@ static inline int cpu_smt_flags(void)
}
#endif

+#ifdef CONFIG_SCHED_CLUSTER
+static inline int cpu_cluster_flags(void)
+{
+ return SD_SHARE_PKG_RESOURCES;
+}
+#endif
+
#ifdef CONFIG_SCHED_MC
static inline int cpu_core_flags(void)
{
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 80d27d7..0b3704a 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -212,6 +212,13 @@ static inline const struct cpumask *cpu_smt_mask(int cpu)
}
#endif

+#if defined(CONFIG_SCHED_CLUSTER) && !defined(cpu_cluster_mask)
+static inline const struct cpumask *cpu_cluster_mask(int cpu)
+{
+ return topology_cluster_cpumask(cpu);
+}
+#endif
+
static inline const struct cpumask *cpu_cpu_mask(int cpu)
{
return cpumask_of_node(cpu_to_node(cpu));
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 28c4df6..19e2536 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7840,6 +7840,17 @@ int sched_cpu_activate(unsigned int cpu)
if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
static_branch_inc_cpuslocked(&sched_smt_present);
#endif
+
+#ifdef CONFIG_SCHED_CLUSTER
+ /*
+ * When going up, increment the number of cluster cpus with
+ * cluster present.
+ */
+ if (cpumask_weight(cpu_cluster_mask(cpu)) > cpumask_weight(cpu_smt_mask(cpu)) &&
+ cpumask_weight(cpu_cluster_mask(cpu)) < cpumask_weight(cpu_coregroup_mask(cpu)))
+ static_branch_inc_cpuslocked(&sched_cluster_present);
+#endif
+
set_cpu_active(cpu, true);

if (sched_smp_initialized) {
@@ -7916,6 +7927,15 @@ int sched_cpu_deactivate(unsigned int cpu)
static_branch_dec_cpuslocked(&sched_smt_present);
#endif

+#ifdef CONFIG_SCHED_CLUSTER
+ /*
+ * When going down, decrement the number of cpus with cluster present.
+ */
+ if (cpumask_weight(cpu_cluster_mask(cpu)) > cpumask_weight(cpu_smt_mask(cpu)) &&
+ cpumask_weight(cpu_cluster_mask(cpu)) < cpumask_weight(cpu_coregroup_mask(cpu)))
+ static_branch_dec_cpuslocked(&sched_cluster_present);
+#endif
+
if (!sched_smp_initialized)
return 0;

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2e2ab1e..c92ad9f2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6021,6 +6021,10 @@ static inline int __select_idle_cpu(int cpu)
return -1;
}

+#ifdef CONFIG_SCHED_CLUSTER
+DEFINE_STATIC_KEY_FALSE(sched_cluster_present);
+#endif
+
#ifdef CONFIG_SCHED_SMT
DEFINE_STATIC_KEY_FALSE(sched_smt_present);
EXPORT_SYMBOL_GPL(sched_smt_present);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d2e09a6..73f7406 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -6,6 +6,7 @@

#include <linux/sched/autogroup.h>
#include <linux/sched/clock.h>
+#include <linux/sched/cluster.h>
#include <linux/sched/coredump.h>
#include <linux/sched/cpufreq.h>
#include <linux/sched/cputime.h>
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 12f8058..ae1fa00 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1511,6 +1511,11 @@ static void claim_allocations(int cpu, struct sched_domain *sd)
#ifdef CONFIG_SCHED_SMT
{ cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },
#endif
+
+#ifdef CONFIG_SCHED_CLUSTER
+ { cpu_clustergroup_mask, cpu_cluster_flags, SD_INIT_NAME(CLS) },
+#endif
+
#ifdef CONFIG_SCHED_MC
{ cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
#endif
--
1.8.3.1