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Message-ID: <54CEDEDC.7060507@gmail.com>
Date: Mon, 02 Feb 2015 10:20:12 +0800
From: Fan Du <fengyuleidian0615@...il.com>
To: Alexander Duyck <alexander.h.duyck@...hat.com>
CC: Fan Du <fan.du@...el.com>, bhutchings@...arflare.com,
davem@...emloft.net, netdev@...r.kernel.org
Subject: [PATCHv2 net] net: restore lro after device detached from bridge
于 2015年01月31日 04:48, Alexander Duyck 写道:
> On 01/30/2015 04:33 AM, Fan Du wrote:
>> Either detaching a device from bridge or switching a device
>> out of FORWARDING state, the original lro feature should
>> possibly be enabled for good reason, e.g. hw feature like
>> receive side coalescing could come into play.
>>
>> BEFORE:
>> echo 1 > /proc/sys/net/ipv4/conf/ens806f0/forwarding && ethtool -k ens806f0 | grep large
>> large-receive-offload: off
>>
>> echo 0 > /proc/sys/net/ipv4/conf/ens806f0/forwarding && ethtool -k ens806f0 | grep large
>> large-receive-offload: off
>>
>> AFTER:
>> echo 1 > /proc/sys/net/ipv4/conf/ens806f0/forwarding && ethtool -k ens806f0 | grep large
>> large-receive-offload: off
>>
>> echo 0 > /proc/sys/net/ipv4/conf/ens806f0/forwarding && ethtool -k ens806f0 | grep large
>> large-receive-offload: on
>>
>> Signed-off-by: Fan Du <fan.du@...el.com>
>> Fixes: 0187bdfb0567 ("net: Disable LRO on devices that are forwarding")
>
> First off this isn't a "fix". This is going to likely break more than
> it fixes. The main reason why LRO is disabled is because it can cause
> more harm then it helps. Since GRO is available we should err on the
> side of caution since enabling LRO/RSC can have undesirable side effects
> in a number of cases.
I think you are talking about bad scenarios when net device is attached to a bridge.
Then what's the good reason user has to pay extra cpu power for using GRO, instead
of using hw capable LRO/RSC when this net device is detached from bridge acting as
a standalone NIC?
Note, SRC is defaulted to *ON* in practice for ALL ixgbe NICs, as same other RSC capable
NICs. Attaching net device to a bridge _once_ should not changed its default configuration,
moreover it's a subtle change without any message that user won't noticed at all.
From 1e76b2625b3e6aa239b5ef8399fe441a587c6646 Mon Sep 17 00:00:00 2001
From: Fan Du <fan.du@...el.com>
Date: Mon, 2 Feb 2015 05:02:11 -0500
Subject: [PATCH] net: restore lro after device detached from bridge
When detached net device from a bridge, the original lro
feature should possibly be enabled for good reason, e.g.
hw feature like receive side coalescing could come into play.
Signed-off-by: Fan Du <fan.du@...el.com>
Fixes: 0187bdfb0567 ("net: Disable LRO on devices that are forwarding")
---
ChangeLog:
v2:
- Restore lro only when device detached from bridge
---
include/linux/netdevice.h | 1 +
net/bridge/br_if.c | 1 +
net/core/dev.c | 23 +++++++++++++++++++++++
3 files changed, 25 insertions(+)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 642d426..904b1a4 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2153,6 +2153,7 @@ int dev_alloc_name(struct net_device *dev, const char *name);
int dev_open(struct net_device *dev);
int dev_close(struct net_device *dev);
void dev_disable_lro(struct net_device *dev);
+void dev_enable_lro(struct net_device *dev);
int dev_loopback_xmit(struct sk_buff *newskb);
int dev_queue_xmit(struct sk_buff *skb);
int dev_queue_xmit_accel(struct sk_buff *skb, void *accel_priv);
diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index 81e49fb..4236f3a 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -565,6 +565,7 @@ int br_del_if(struct net_bridge *br, struct net_device *dev)
call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);
netdev_update_features(br->dev);
+ dev_enable_lro(dev);
return 0;
}
diff --git a/net/core/dev.c b/net/core/dev.c
index 1e325ad..76f2ed7 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1451,6 +1451,29 @@ void dev_disable_lro(struct net_device *dev)
}
EXPORT_SYMBOL(dev_disable_lro);
+/**
+ * dev_enable_lro - enable Large Receive Offload on a device
+ * @dev: device
+ *
+ * Enable Large Receive Offload (LRO) on a net device.
+ * This is needed if device is not attached to a bridge.
+ */
+void dev_enable_lro(struct net_device *dev)
+{
+ struct net_device *lower_dev;
+ struct list_head *iter;
+
+ dev->wanted_features |= NETIF_F_LRO;
+ netdev_update_features(dev);
+
+ if (unlikely(!(dev->features & NETIF_F_LRO)))
+ netdev_WARN(dev, "failed to enable LRO!\n");
+
+ netdev_for_each_lower_dev(dev, lower_dev, iter)
+ dev_enable_lro(lower_dev);
+}
+EXPORT_SYMBOL(dev_enable_lro);
+
static int call_netdevice_notifier(struct notifier_block *nb, unsigned long val,
struct net_device *dev)
{
--
1.8.3.1
> As far as the rest of the patch I have serious misgivings as this is
> going to be switching on LRO in multiple cases so if the user disables
> it they will find it was re-enabled when they likely weren't expecting
> it. LRO/RSC has a history of causing issues in a number of different
> cases. I'd say if it is off leave it off. If the user really wants to
> enable it they can do so via the ethtool interface that is already
> provided in the kernel after they have removed the interface from the
> bridge, or disabled IP routing.
>
> Leaving it disabled would be consistent with how it is handled in
> ixgbe_fix_features when Rx checksum offload is disabled. We just
> disable the feature and expect the user to re-enable it when they
> re-enable Rx checksum offload. The same logic should apply here. The
> user put the hardware in this state, it is the responsibility of the
> user to sort out the side effects of disabled features after they revert
> to their original state.
>> ---
>> include/linux/netdevice.h | 1 +
>> net/bridge/br_if.c | 1 +
>> net/core/dev.c | 24 ++++++++++++++++++++++++
>> net/ipv4/devinet.c | 4 ++++
>> net/ipv6/addrconf.c | 2 ++
>> 5 files changed, 32 insertions(+)
>>
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index 642d426..904b1a4 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -2153,6 +2153,7 @@ int dev_alloc_name(struct net_device *dev, const char *name);
>> int dev_open(struct net_device *dev);
>> int dev_close(struct net_device *dev);
>> void dev_disable_lro(struct net_device *dev);
>> +void dev_enable_lro(struct net_device *dev);
>> int dev_loopback_xmit(struct sk_buff *newskb);
>> int dev_queue_xmit(struct sk_buff *skb);
>> int dev_queue_xmit_accel(struct sk_buff *skb, void *accel_priv);
>> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
>> index 81e49fb..4236f3a 100644
>> --- a/net/bridge/br_if.c
>> +++ b/net/bridge/br_if.c
>> @@ -565,6 +565,7 @@ int br_del_if(struct net_bridge *br, struct net_device *dev)
>> call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);
>> netdev_update_features(br->dev);
>> + dev_enable_lro(dev);
>> return 0;
>> }
>
> Removing an interface from a bridge should not be grounds for turning on LRO/RSC.
>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 1e325ad..938d7f6 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -1451,6 +1451,30 @@ void dev_disable_lro(struct net_device *dev)
>> }
>> EXPORT_SYMBOL(dev_disable_lro);
>> +/**
>> + * dev_enable_lro - enable Large Receive Offload on a device
>> + * @dev: device
>> + *
>> + * Enable Large Receive Offload (LRO) on a net device. Must be
>> + * called under RTNL. This is needed if device is not attached
>> + * to a bridge, or user change the forwarding state.
>> + */
>> +void dev_enable_lro(struct net_device *dev)
>> +{
>> + struct net_device *lower_dev;
>> + struct list_head *iter;
>> +
>> + dev->wanted_features |= NETIF_F_LRO;
>> + netdev_update_features(dev);
>> +
>> + if (unlikely(!(dev->features & NETIF_F_LRO)))
>> + netdev_WARN(dev, "failed to enable LRO!\n");
>> +
>> + netdev_for_each_lower_dev(dev, lower_dev, iter)
>> + dev_enable_lro(lower_dev);
>> +}
>> +EXPORT_SYMBOL(dev_enable_lro);
>> +
>> static int call_netdevice_notifier(struct notifier_block *nb, unsigned long val,
>> struct net_device *dev)
>> {
>> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
>> index 214882e..3307196 100644
>> --- a/net/ipv4/devinet.c
>> +++ b/net/ipv4/devinet.c
>> @@ -1956,6 +1956,8 @@ static void inet_forward_change(struct net *net)
>> struct in_device *in_dev;
>> if (on)
>> dev_disable_lro(dev);
>> + else
>> + dev_enable_lro(dev);
>> rcu_read_lock();
>> in_dev = __in_dev_get_rcu(dev);
>> if (in_dev) {
>
> Disabling it due to a feature conflict makes sense. Enabling it after disabling forwarding not so much. If the user disabled it prior to enabling forwarding it should stay disabled, not be enabled.
>
>> @@ -2047,6 +2049,8 @@ static int devinet_sysctl_forward(struct ctl_table *ctl, int write,
>> container_of(cnf, struct in_device, cnf);
>> if (*valp)
>> dev_disable_lro(idev->dev);
>> + else
>> + dev_enable_lro(idev->dev);
>> inet_netconf_notify_devconf(net,
>> NETCONFA_FORWARDING,
>> idev->dev->ifindex,
>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
>> index f7c8bbe..4c3b54c 100644
>> --- a/net/ipv6/addrconf.c
>> +++ b/net/ipv6/addrconf.c
>> @@ -669,6 +669,8 @@ static void dev_forward_change(struct inet6_dev *idev)
>> dev = idev->dev;
>> if (idev->cnf.forwarding)
>> dev_disable_lro(dev);
>> + else
>> + dev_enable_lro(dev);
>> if (dev->flags & IFF_MULTICAST) {
>> if (idev->cnf.forwarding) {
>> ipv6_dev_mc_inc(dev, &in6addr_linklocal_allrouters);
>
> Same applies here.
>
> If anything this patch seems like more of a feature request then a fix. It would likely create a desirable effect for some, but have some undesirable side-effects for other users.
>
> - Alex
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