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kernel: add a RPS balancer

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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>
This commit is contained in:
John Crispin 2018-08-13 16:24:17 +02:00
parent 8e9a59a6b9
commit 7af1fb9faa
1 changed files with 93 additions and 0 deletions
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93
target/linux/generic/hack-4.14/600-net-core-add-RPS-balancer.patch Normal file
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@ -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