[PATCH v6 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path
Yicong Yang
yangyicong at huawei.com
Tue Jul 26 00:47:58 PDT 2022
From: Barry Song <song.bao.hua at 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.
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/sched/core patched
Hmean 1 345.89 ( 0.00%) 398.43 * 15.19%*
Hmean 2 697.77 ( 0.00%) 794.40 * 13.85%*
Hmean 4 1392.51 ( 0.00%) 1577.60 * 13.29%*
Hmean 8 2800.61 ( 0.00%) 3118.38 * 11.35%*
Hmean 16 5514.27 ( 0.00%) 6124.51 * 11.07%*
Hmean 32 10869.81 ( 0.00%) 10690.97 * -1.65%*
Hmean 64 8315.22 ( 0.00%) 8520.73 * 2.47%*
Hmean 128 6324.47 ( 0.00%) 7253.65 * 14.69%*
On numa 0-1:
tip/sched/core patched
Hmean 1 348.68 ( 0.00%) 397.74 * 14.07%*
Hmean 2 693.57 ( 0.00%) 795.54 * 14.70%*
Hmean 4 1369.26 ( 0.00%) 1548.72 * 13.11%*
Hmean 8 2772.99 ( 0.00%) 3055.54 * 10.19%*
Hmean 16 4825.83 ( 0.00%) 5936.64 * 23.02%*
Hmean 32 10250.32 ( 0.00%) 11780.59 * 14.93%*
Hmean 64 16309.51 ( 0.00%) 19864.38 * 21.80%*
Hmean 128 13022.32 ( 0.00%) 16365.43 * 25.67%*
Hmean 256 11335.79 ( 0.00%) 13991.33 * 23.43%*
Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so the SMT branch
in the code has not been tested but it supposed to work.
Suggested-by: Peter Zijlstra <peterz at infradead.org>
[https://lore.kernel.org/lkml/Ytfjs+m1kUs0ScSn@worktop.programming.kicks-ass.net]
Tested-by: Yicong Yang <yangyicong at hisilicon.com>
Signed-off-by: Barry Song <song.bao.hua at hisilicon.com>
Signed-off-by: Yicong Yang <yangyicong at hisilicon.com>
Reviewed-by: Tim Chen <tim.c.chen at linux.intel.com>
---
kernel/sched/fair.c | 31 ++++++++++++++++++++++++++++---
kernel/sched/sched.h | 2 ++
kernel/sched/topology.c | 10 ++++++++++
3 files changed, 40 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2fc47257ae91..1100fbf7baaf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6437,6 +6437,31 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
}
}
+ if (IS_ENABLED(CONFIG_SCHED_CLUSTER) &&
+ static_branch_unlikely(&sched_cluster_active)) {
+ struct sched_domain *sdc = rcu_dereference(per_cpu(sd_cluster, target));
+
+ if (sdc) {
+ for_each_cpu_wrap(cpu, sched_domain_span(sdc), target + 1) {
+ if (!cpumask_test_cpu(cpu, cpus))
+ continue;
+
+ if (has_idle_core) {
+ i = select_idle_core(p, cpu, cpus, &idle_cpu);
+ if ((unsigned int)i < nr_cpumask_bits)
+ return i;
+ } else {
+ if (--nr <= 0)
+ 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(sdc));
+ }
+ }
+
for_each_cpu_wrap(cpu, cpus, target + 1) {
if (has_idle_core) {
i = select_idle_core(p, cpu, cpus, &idle_cpu);
@@ -6444,7 +6469,7 @@ 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)
@@ -6543,7 +6568,7 @@ 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;
@@ -6569,7 +6594,7 @@ 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)) {
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 845cd029d572..4f0d3a74a532 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1808,7 +1808,9 @@ 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);
+
extern struct static_key_false sched_asym_cpucapacity;
+extern struct static_key_false sched_cluster_active;
struct sched_group_capacity {
atomic_t ref;
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8ab27c0d6d1f..04ead3227201 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -670,7 +670,9 @@ 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);
DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
+
DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
+DEFINE_STATIC_KEY_FALSE(sched_cluster_active);
static void update_top_cache_domain(int cpu)
{
@@ -2268,6 +2270,7 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
struct rq *rq = NULL;
int i, ret = -ENOMEM;
bool has_asym = false;
+ bool has_cluster = false;
if (WARN_ON(cpumask_empty(cpu_map)))
goto error;
@@ -2289,6 +2292,7 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
sd = build_sched_domain(tl, cpu_map, attr, sd, i);
has_asym |= sd->flags & SD_ASYM_CPUCAPACITY;
+ has_cluster |= sd->flags & SD_CLUSTER;
if (tl == sched_domain_topology)
*per_cpu_ptr(d.sd, i) = sd;
@@ -2399,6 +2403,9 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
if (has_asym)
static_branch_inc_cpuslocked(&sched_asym_cpucapacity);
+ if (has_cluster)
+ static_branch_inc_cpuslocked(&sched_cluster_active);
+
if (rq && sched_debug_verbose) {
pr_info("root domain span: %*pbl (max cpu_capacity = %lu)\n",
cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
@@ -2498,6 +2505,9 @@ static void detach_destroy_domains(const struct cpumask *cpu_map)
if (rcu_access_pointer(per_cpu(sd_asym_cpucapacity, cpu)))
static_branch_dec_cpuslocked(&sched_asym_cpucapacity);
+ if (rcu_access_pointer(per_cpu(sd_cluster, cpu)))
+ static_branch_dec_cpuslocked(&sched_cluster_active);
+
rcu_read_lock();
for_each_cpu(i, cpu_map)
cpu_attach_domain(NULL, &def_root_domain, i);
--
2.24.0
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