xfrm: policy: remove pcpu policy cache

Kristian Evensen says:
  In a project I am involved in, we are running ipsec (Strongswan) on
  different mt7621-based routers. Each router is configured as an
  initiator and has around ~30 tunnels to different responders (running
  on misc. devices). Before the flow cache was removed (kernel 4.9), we
  got a combined throughput of around 70Mbit/s for all tunnels on one
  router. However, we recently switched to kernel 4.14 (4.14.48), and
  the total throughput is somewhere around 57Mbit/s (best-case). I.e., a
  drop of around 20%. Reverting the flow cache removal restores, as
  expected, performance levels to that of kernel 4.9.

When pcpu xdst exists, it has to be validated first before it can be
used.

A negative hit thus increases cost vs. no-cache.

As number of tunnels increases, hit rate decreases so this pcpu caching
isn't a viable strategy.

Furthermore, the xdst cache also needs to run with BH off, so when
removing this the bh disable/enable pairs can be removed too.

Kristian tested a 4.14.y backport of this change and reported
increased performance:

  In our tests, the throughput reduction has been reduced from around -20%
  to -5%. We also see that the overall throughput is independent of the
  number of tunnels, while before the throughput was reduced as the number
  of tunnels increased.

Reported-by: Kristian Evensen <kristian.evensen@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

1 files changed, 0 insertions, 10 deletions

diff --git a/net/xfrm/xfrm_device.c b/net/xfrm/xfrm_device.c
index 16c1230d20fa..11d56a44e9e8 100644
--- a/net/xfrm/xfrm_device.c
+++ b/net/xfrm/xfrm_device.c
@@ -307,12 +307,6 @@ static int xfrm_dev_register(struct net_device *dev)
 	return xfrm_api_check(dev);
 }
 
-static int xfrm_dev_unregister(struct net_device *dev)
-{
-	xfrm_policy_cache_flush();
-	return NOTIFY_DONE;
-}
-
 static int xfrm_dev_feat_change(struct net_device *dev)
 {
 	return xfrm_api_check(dev);
@@ -323,7 +317,6 @@ static int xfrm_dev_down(struct net_device *dev)
 	if (dev->features & NETIF_F_HW_ESP)
 		xfrm_dev_state_flush(dev_net(dev), dev, true);
 
-	xfrm_policy_cache_flush();
 	return NOTIFY_DONE;
 }
 
@@ -335,9 +328,6 @@ static int xfrm_dev_event(struct notifier_block *this, unsigned long event, void
 	case NETDEV_REGISTER:
 		return xfrm_dev_register(dev);
 
-	case NETDEV_UNREGISTER:
-		return xfrm_dev_unregister(dev);
-
 	case NETDEV_FEAT_CHANGE:
 		return xfrm_dev_feat_change(dev);