From:   Yicong Yang <yangyicong@hisilicon.com>
To:     <peterz@infradead.org>, <mingo@redhat.com>,
        <juri.lelli@redhat.com>, <vincent.guittot@linaro.org>,
        <tim.c.chen@linux.intel.com>, <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
CC:     <dietmar.eggemann@arm.com>, <rostedt@goodmis.org>,
        <bsegall@google.com>, <bristot@redhat.com>,
        <prime.zeng@huawei.com>, <yangyicong@hisilicon.com>,
        <jonathan.cameron@huawei.com>, <ego@linux.vnet.ibm.com>,
        <srikar@linux.vnet.ibm.com>, <linuxarm@huawei.com>,
        <21cnbao@gmail.com>, <song.bao.hua@hisilicon.com>,
        <guodong.xu@linaro.org>
Subject: [PATCH 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path
Date:   Wed, 15 Dec 2021 12:11:49 +0800
Message-ID: <20211215041149.73171-3-yangyicong@hisilicon.com>
In-Reply-To: <20211215041149.73171-1-yangyicong@hisilicon.com>
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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. 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@hisilicon.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Yicong Yang <yangyicong@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