From: Peter Nørlund <pch@xxxxxxxxxxxx>
The current multipath attempted to be quasi random, but in most cases it
behaved just like a round robin balancing. This patch refactors the
algorithm to be exactly that and in doing so, avoids the spin lock.
The new design paves the way for hash-based multipath, replacing the
modulo with thresholds, minimizing disruption in case of failing paths or
route replacements.
Signed-off-by: Peter Nørlund <pch@xxxxxxxxxxxx>
---
include/net/ip_fib.h | 4 +-
net/ipv4/Kconfig | 1 +
net/ipv4/fib_semantics.c | 129 ++++++++++++++++++++++++++---------------------
3 files changed, 74 insertions(+), 60 deletions(-)
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index a37d043..18a3c7f 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -79,7 +79,7 @@ struct fib_nh {
unsigned char nh_scope;
#ifdef CONFIG_IP_ROUTE_MULTIPATH
int nh_weight;
- int nh_power;
+ atomic_t nh_upper_bound;
#endif
#ifdef CONFIG_IP_ROUTE_CLASSID
__u32 nh_tclassid;
@@ -118,7 +118,7 @@ struct fib_info {
#define fib_advmss fib_metrics[RTAX_ADVMSS-1]
int fib_nhs;
#ifdef CONFIG_IP_ROUTE_MULTIPATH
- int fib_power;
+ int fib_weight;
#endif
struct rcu_head rcu;
struct fib_nh fib_nh[0];
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 416dfa0..23d8b2b 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -81,6 +81,7 @@ config IP_MULTIPLE_TABLES
config IP_ROUTE_MULTIPATH
bool "IP: equal cost multipath"
depends on IP_ADVANCED_ROUTER
+ select BITREVERSE
help
Normally, the routing tables specify a single action to be taken in
a deterministic manner for a given packet. If you say Y here
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 1b2d011..becb63f 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -15,6 +15,7 @@
#include <asm/uaccess.h>
#include <linux/bitops.h>
+#include <linux/bitrev.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/jiffies.h>
@@ -58,7 +59,7 @@ static struct hlist_head fib_info_devhash[DEVINDEX_HASHSIZE];
#ifdef CONFIG_IP_ROUTE_MULTIPATH
-static DEFINE_SPINLOCK(fib_multipath_lock);
+static DEFINE_PER_CPU(int, fib_multipath_rr_counter);
#define for_nexthops(fi) { \
int nhsel; const struct fib_nh *nh; \
@@ -468,6 +469,52 @@ static int fib_count_nexthops(struct rtnexthop *rtnh, int remaining)
return remaining > 0 ? 0 : nhs;
}
+static void fib_rebalance(struct fib_info *fi)
+{
+ int total;
+ int w;
+ struct in_device *in_dev;
+
+ if (fi->fib_nhs < 2)
+ return;
+
+ total = 0;
+ for_nexthops(fi) {
+ if (nh->nh_flags & RTNH_F_DEAD)
+ continue;
+
+ in_dev = __in_dev_get_rcu(nh->nh_dev);
+
+ if (in_dev &&
+ IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&
+ nh->nh_flags & RTNH_F_LINKDOWN)
+ continue;
+
+ total += nh->nh_weight;
+ } endfor_nexthops(fi);
+
+ w = 0;
+ change_nexthops(fi) {
+ int upper_bound;
+
+ in_dev = __in_dev_get_rcu(nexthop_nh->nh_dev);
+
+ if (nexthop_nh->nh_flags & RTNH_F_DEAD) {
+ upper_bound = -1;
+ } else if (in_dev &&
+ IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&
+ nexthop_nh->nh_flags & RTNH_F_LINKDOWN) {
+ upper_bound = -1;
+ } else {
+ w += nexthop_nh->nh_weight;
+ upper_bound = DIV_ROUND_CLOSEST(2147483648LL * w,
+ total) - 1;
+ }
+
+ atomic_set(&nexthop_nh->nh_upper_bound, upper_bound);
+ } endfor_nexthops(fi);
+}
+
static int fib_get_nhs(struct fib_info *fi, struct rtnexthop *rtnh,
int remaining, struct fib_config *cfg)
{
@@ -1077,8 +1124,15 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
change_nexthops(fi) {
fib_info_update_nh_saddr(net, nexthop_nh);
+#ifdef CONFIG_IP_ROUTE_MULTIPATH
+ fi->fib_weight += nexthop_nh->nh_weight;
+#endif
} endfor_nexthops(fi)
+#ifdef CONFIG_IP_ROUTE_MULTIPATH
+ fib_rebalance(fi);
+#endif
+
link_it:
ofi = fib_find_info(fi);
if (ofi) {
@@ -1300,12 +1354,6 @@ int fib_sync_down_dev(struct net_device *dev, unsigned long event)
nexthop_nh->nh_flags |= RTNH_F_LINKDOWN;
break;
}
-#ifdef CONFIG_IP_ROUTE_MULTIPATH
- spin_lock_bh(&fib_multipath_lock);
- fi->fib_power -= nexthop_nh->nh_power;
- nexthop_nh->nh_power = 0;
- spin_unlock_bh(&fib_multipath_lock);
-#endif
dead++;
}
#ifdef CONFIG_IP_ROUTE_MULTIPATH
@@ -1328,6 +1376,10 @@ int fib_sync_down_dev(struct net_device *dev, unsigned long event)
}
ret++;
}
+
+#ifdef CONFIG_IP_ROUTE_MULTIPATH
+ fib_rebalance(fi);
+#endif
}
return ret;
@@ -1450,20 +1502,17 @@ int fib_sync_up(struct net_device *dev, unsigned int nh_flags)
!__in_dev_get_rtnl(dev))
continue;
alive++;
-#ifdef CONFIG_IP_ROUTE_MULTIPATH
- spin_lock_bh(&fib_multipath_lock);
- nexthop_nh->nh_power = 0;
- nexthop_nh->nh_flags &= ~nh_flags;
- spin_unlock_bh(&fib_multipath_lock);
-#else
nexthop_nh->nh_flags &= ~nh_flags;
-#endif
} endfor_nexthops(fi)
if (alive > 0) {
fi->fib_flags &= ~nh_flags;
ret++;
}
+
+#ifdef CONFIG_IP_ROUTE_MULTIPATH
+ fib_rebalance(fi);
+#endif
}
return ret;
@@ -1478,55 +1527,19 @@ int fib_sync_up(struct net_device *dev, unsigned int nh_flags)
void fib_select_multipath(struct fib_result *res)
{
struct fib_info *fi = res->fi;
- struct in_device *in_dev;
- int w;
-
- spin_lock_bh(&fib_multipath_lock);
- if (fi->fib_power <= 0) {
- int power = 0;
- change_nexthops(fi) {
- in_dev = __in_dev_get_rcu(nexthop_nh->nh_dev);
- if (nexthop_nh->nh_flags & RTNH_F_DEAD)
- continue;
- if (in_dev &&
- IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&
- nexthop_nh->nh_flags & RTNH_F_LINKDOWN)
- continue;
- power += nexthop_nh->nh_weight;
- nexthop_nh->nh_power = nexthop_nh->nh_weight;
- } endfor_nexthops(fi);
- fi->fib_power = power;
- if (power <= 0) {
- spin_unlock_bh(&fib_multipath_lock);
- /* Race condition: route has just become dead. */
- res->nh_sel = 0;
- return;
- }
- }
+ int h;
+ h = bitrev32(this_cpu_inc_return(fib_multipath_rr_counter)) >> 1;
- /* w should be random number [0..fi->fib_power-1],
- * it is pretty bad approximation.
- */
-
- w = jiffies % fi->fib_power;
+ for_nexthops(fi) {
+ if (h > atomic_read(&nh->nh_upper_bound))
+ continue;
- change_nexthops(fi) {
- if (!(nexthop_nh->nh_flags & RTNH_F_DEAD) &&
- nexthop_nh->nh_power) {
- w -= nexthop_nh->nh_power;
- if (w <= 0) {
- nexthop_nh->nh_power--;
- fi->fib_power--;
- res->nh_sel = nhsel;
- spin_unlock_bh(&fib_multipath_lock);
- return;
- }
- }
- } endfor_nexthops(fi);
+ res->nh_sel = nhsel;
+ return;
+ } endfor_nexthops(fi)
/* Race condition: route has just become dead. */
res->nh_sel = 0;
- spin_unlock_bh(&fib_multipath_lock);
}
#endif
--
2.1.4
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