kernel: add a RPS balancer

By default the RPS delegation will happen by masking the last few bits of skb->hash. This patch adds an inermediate hash bucket that maps the masked hash to a RPS core. This makes RPS results much more deterministic on SMP systems. Signed-off-by: John Crispin <john@phrozen.org>
6 years ago · 7af1fb9faa
parent 8e9a59a6b9
commit 7af1fb9faa
1 changed files with 93 additions and 0 deletions
--- a/target/linux/generic/hack-4.14/600-net-core-add-RPS-balancer.patch
+++ b/target/linux/generic/hack-4.14/600-net-core-add-RPS-balancer.patch
@ -0,0 +1,93 @@
+From 3e969c9695b45e1a052d43b367096ec99f2f0aac Mon Sep 17 00:00:00 2001
+From: John Crispin <john@phrozen.org>
+Date: Thu, 10 Aug 2017 15:58:29 +0200
+Subject: [PATCH] net: core: add RPS balancer
+
+This patch adds a hash bucket based rps hash balancer.
+
+Signed-off-by: John Crispin <john@phrozen.org>
+---
+ net/core/dev.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
+ 1 file changed, 56 insertions(+), 1 deletion(-)
+
+--- a/net/core/dev.c
+++ b/net/core/dev.c
+@@ -3626,6 +3626,58 @@ set_rps_cpu(struct net_device *dev, stru
+ 	return rflow;
+ }
+ 
+#define RPS_TBL_SIZE_SHIFT	10
+#define RPS_TBL_SIZE		(1 << RPS_TBL_SIZE_SHIFT)
+struct rps_table {
+	int			core;
+	struct timer_list	expire;
+};
+static struct rps_table rps_table[RPS_TBL_SIZE];
+static int rps_table_last_core;
+
+static void rps_table_expire(unsigned long data)
+{
+	struct rps_table *entry = (struct rps_table *) data;
+
+	entry->core = -1;
+}
+
+static int rps_table_core(struct rps_map *map)
+{
+	int i;
+
+	for (i = 0; i < map->len; i++) {
+		int cpu = map->cpus[(rps_table_last_core + i + 1) % map->len];
+		if (cpu_online(cpu)) {
+			rps_table_last_core = cpu;
+			return cpu;
+		}
+	}
+	return map->cpus[0];
+}
+
+static int rps_table_lookup(struct rps_map *map, u32 hash)
+{
+	int bucket = hash & 0x3ff;
+
+	if (rps_table[bucket].core < 0)
+		rps_table[bucket].core = rps_table_core(map);
+	mod_timer(&rps_table[bucket].expire, jiffies + HZ);
+
+	return rps_table[bucket].core;
+}
+
+static void rps_table_init(void)
+{
+	int i;
+
+	for (i = 0; i < RPS_TBL_SIZE; i++) {
+		rps_table[i].core = -1;
+		setup_timer(&rps_table[i].expire, rps_table_expire,
+			    (unsigned long) &rps_table[i]);
+	}
+}
+
+ /*
+  * get_rps_cpu is called from netif_receive_skb and returns the target
+  * CPU from the RPS map of the receiving queue for a given skb.
+@@ -3715,7 +3767,7 @@ static int get_rps_cpu(struct net_device
+ try_rps:
+ 
+ 	if (map) {
+-		tcpu = map->cpus[reciprocal_scale(hash, map->len)];
+		tcpu = rps_table_lookup(map, hash);
+ 		if (cpu_online(tcpu)) {
+ 			cpu = tcpu;
+ 			goto done;
+@@ -8800,6 +8852,10 @@ static int __init net_dev_init(void)
+ 		sd->backlog.weight = weight_p;
+ 	}
+ 
+#ifdef CONFIG_RPS
+		rps_table_init();
+#endif
+
+ 	dev_boot_phase = 0;
+ 
+ 	/* The loopback device is special if any other network devices