[PATCH v2 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path
Yicong Yang
yangyicong at hisilicon.com
Wed Jan 26 00:09:47 PST 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.
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:
5.17-rc1 patched
Hmean 1 324.73 ( 0.00%) 378.01 * 16.41%*
Hmean 2 645.36 ( 0.00%) 754.63 * 16.93%*
Hmean 4 1302.09 ( 0.00%) 1507.54 * 15.78%*
Hmean 8 2612.03 ( 0.00%) 2982.57 * 14.19%*
Hmean 16 5307.12 ( 0.00%) 5886.66 * 10.92%*
Hmean 32 9354.22 ( 0.00%) 9908.13 * 5.92%*
Hmean 64 7240.35 ( 0.00%) 7278.78 * 0.53%*
Hmean 128 6186.40 ( 0.00%) 6187.85 ( 0.02%)
On numa 0-1:
5.17-rc1 patched
Hmean 1 320.01 ( 0.00%) 378.44 * 18.26%*
Hmean 2 643.85 ( 0.00%) 752.52 * 16.88%*
Hmean 4 1287.36 ( 0.00%) 1505.62 * 16.95%*
Hmean 8 2564.60 ( 0.00%) 2955.29 * 15.23%*
Hmean 16 5195.69 ( 0.00%) 5814.74 * 11.91%*
Hmean 32 9769.16 ( 0.00%) 10872.63 * 11.30%*
Hmean 64 15952.50 ( 0.00%) 17281.98 * 8.33%*
Hmean 128 13113.77 ( 0.00%) 13895.20 * 5.96%*
Hmean 256 10997.59 ( 0.00%) 11244.69 * 2.25%*
Hmean 512 14623.60 ( 0.00%) 15526.25 * 6.17%*
This will also help to improve the MySQL. With MySQL server
running on numa 0 and client running on numa 1, both QPS and
latency is imporved on read-write case:
5.17-rc1 patched
QPS-16threads 143333.2633 145077.4033(+1.22%)
QPS-24threads 195085.9367 202719.6133(+3.91%)
QPS-32threads 241165.6867 249020.74(+3.26%)
QPS-64threads 244586.8433 253387.7567(+3.60%)
avg-lat-16threads 2.23 2.19(+1.19%)
avg-lat-24threads 2.46 2.36(+3.79%)
avg-lat-36threads 2.66 2.57(+3.26%)
avg-lat-64threads 5.23 5.05(+3.44%)
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>
---
kernel/sched/fair.c | 46 +++++++++++++++++++++++++++++++++++++++++----
1 file changed, 42 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5146163bfabb..2f84a933aedd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6262,12 +6262,46 @@ 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, int prev_cpu, int target)
+{
+ struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
+ struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target));
+ int cpu, idle_cpu;
+
+ /* TODO: Support SMT case while a machine with both cluster and SMT born */
+ if (!sched_smt_active() && sd) {
+ for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
+ idle_cpu = __select_idle_cpu(cpu, p);
+ if ((unsigned int)idle_cpu < nr_cpumask_bits)
+ return idle_cpu;
+ }
+
+ /* Don't ping-pong tasks in and out cluster frequently */
+ if (cpus_share_resources(target, prev_cpu))
+ return target;
+
+ cpumask_andnot(cpus, cpus, sched_domain_span(sd));
+ }
+
+ return -1;
+}
+#else
+static inline int scan_cluster(struct task_struct *p, int prev_cpu, int target)
+{
+ 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
* average idle time for this rq (as found in rq->avg_idle).
*/
-static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool has_idle_core, int target)
+static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool has_idle_core, int prev_cpu, int target)
{
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
int i, cpu, idle_cpu = -1, nr = INT_MAX;
@@ -6282,6 +6316,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+ idle_cpu = scan_cluster(p, prev_cpu, target);
+ if ((unsigned int)idle_cpu < nr_cpumask_bits)
+ return idle_cpu;
+
if (sched_feat(SIS_PROP) && !has_idle_core) {
u64 avg_cost, avg_idle, span_avg;
unsigned long now = jiffies;
@@ -6416,7 +6454,7 @@ 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_resources(prev, target) &&
(available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
asym_fits_capacity(task_util, prev))
return prev;
@@ -6442,7 +6480,7 @@ 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_resources(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)) {
@@ -6483,7 +6521,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
}
}
- i = select_idle_cpu(p, sd, has_idle_core, target);
+ i = select_idle_cpu(p, sd, has_idle_core, prev, target);
if ((unsigned)i < nr_cpumask_bits)
return i;
--
2.24.0
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