[PATCH 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path
Yicong Yang
yangyicong at hisilicon.com
Tue Dec 14 20:11:49 PST 2021
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. 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:
5.16-rc1 patched
Hmean 1 329.17 ( 0.00%) 384.84 * 16.91%*
Hmean 2 654.09 ( 0.00%) 768.77 * 17.53%*
Hmean 4 1321.41 ( 0.00%) 1538.10 * 16.40%*
Hmean 8 2650.43 ( 0.00%) 3048.86 * 15.03%*
Hmean 16 5322.37 ( 0.00%) 5975.20 * 12.27%*
Hmean 32 10002.11 ( 0.00%) 10085.57 * 0.83%*
Hmean 64 7910.39 ( 0.00%) 7936.37 * 0.33%*
Hmean 128 6745.25 ( 0.00%) 6811.28 * 0.98%*
On numa 0-1:
5.16-rc1 patched
Hmean 1 326.61 ( 0.00%) 385.36 * 17.99%*
Hmean 2 650.62 ( 0.00%) 770.57 * 18.44%*
Hmean 4 1318.05 ( 0.00%) 1534.83 * 16.45%*
Hmean 8 2621.50 ( 0.00%) 3030.10 * 15.59%*
Hmean 16 5252.17 ( 0.00%) 6023.08 * 14.68%*
Hmean 32 9829.30 ( 0.00%) 9856.33 * 0.28%*
Hmean 64 12452.66 ( 0.00%) 17338.48 * 39.24%*
Hmean 128 14181.24 ( 0.00%) 15025.24 * 5.95%*
Hmean 256 12239.07 ( 0.00%) 13080.16 * 6.87%*
Hmean 512 14297.00 ( 0.00%) 15063.76 * 5.36%*
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:
5.16-rc1 patched
QPS-24threads 195327.48 202081.28(+3.46%)
QPS-32threads 242039.4 247059.5(+2.07%)
QPS-64threads 243024.52 254274.47(+4.63%)
avg-lat-24threads 2.46 2.37(+3.66%)
avg-lat-36threads 2.64 2.59(+1.89%)
avg-lat-64threads 5.27 5.03(+4.55%)
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 6e476f6d9435..8a5795c78af8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6230,12 +6230,46 @@ 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_cluster(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;
@@ -6250,6 +6284,10 @@ 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;
@@ -6384,7 +6422,7 @@ 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_cluster(prev, target) &&
(available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
asym_fits_capacity(task_util, prev))
return prev;
@@ -6408,7 +6446,7 @@ 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_cluster(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)) {
@@ -6449,7 +6487,7 @@ 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;
--
2.33.0
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