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Re: [RFC PATCH net-next] net/core: initial support for stacked dev feature toggles

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Alexander Duyck wrote:
> On 10/23/2015 08:40 PM, Jarod Wilson wrote:
>> There are some netdev features that make little sense to toggle on and
>> off in a stacked device setup on only one device in the stack. The prime
>> example is a bonded connection, where it really doesn't make sense to
>> disable LRO on the master, but not on any of the slaves, nor does it
>> really make sense to be able to shut LRO off on a slave when its still
>> enabled on the master.
>>
>> The strategy here is to add a section near the end of
>> netdev_fix_features() that looks for upper and lower netdevs, then make
>> sure certain feature flags match both up and down the stack. At present,
>> only the LRO flag is included.
...
>> +static void netdev_sync_lower_features(struct net_device *upper,
>> + struct net_device *lower, netdev_features_t features)
>> +{
>> + netdev_features_t want = features & lower->hw_features;
>> +
>> + if (!(features & NETIF_F_LRO) && (lower->features & NETIF_F_LRO)) {
>> + netdev_info(upper, "Disabling LRO on lower dev %s.\n",
>> + lower->name);
>> + upper->wanted_features &= ~NETIF_F_LRO;
>> + lower->wanted_features &= ~NETIF_F_LRO;
>> + netdev_update_features(lower);
>> + if (unlikely(lower->features & NETIF_F_LRO))
>> + netdev_WARN(upper, "failed to disable LRO on %s!\n",
>> + lower->name);
>> + } else if ((want & NETIF_F_LRO) && !(lower->features & NETIF_F_LRO)) {
>> + netdev_info(upper, "Enabling LRO on lower dev %s.\n",
>> + lower->name);
>> + upper->wanted_features |= NETIF_F_LRO;
>> + lower->wanted_features |= NETIF_F_LRO;
>> + netdev_update_features(lower);
>> + if (unlikely(!(lower->features & NETIF_F_LRO)))
>> + netdev_WARN(upper, "failed to enable LRO on %s!\n",
>> + lower->name);
>> + }
>> +}
>> +
>
> Same thing here. If a lower dev has it disabled then leave it disabled.
> I believe your goal is to make it so that dev_disable_lro() can shut
> down LRO when it is making packets in the data-path unusable. There is
> no need to make this an all or nothing scenario. We can let the stack
> slam things down with dev_disable_lro() and then if a user so desires
> they can come back through and enable LRO more selectively if they for
> instance have an interface that can do a smarter job of putting together
> frames that could be routed.
>
> You could probably look at doing something like this for RXCSUM as well.
> The general idea is that if an upper device has it off then the value
> has to be off. For example if RXCSUM is off in a upper device and LRO is
> enabled on the lower device there is a good chance that the upper device
> will report checksum errors since most LRO implementations don't
> recalculate the checksum. If RXCSUM is forced down to the lower device
> hopefully its fix_features will know this and disable LRO on that device
> when the RXCSUM is disabled on it.

Yeah, I was thinking there might be more flags to treat the same way, 
just wanted to hammer out the plausibility of doing it at all first. I 
can add RXCSUM to v2, or just wait until there's something that people 
might consider merge-worthy before worrying about additional flags. From 
what I've seen, most device's fix_features are reasonably intelligent 
about allowing/disallowing certain flag combos, so this does look pretty 
safe at a glance, and if a specific device tips over, it probably needs 
to be fixed in the device's driver anyway.

-- 
Jarod Wilson
jarod@redhat.com


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[RFC PATCH net-next] net/core: initial support for stacked dev feature toggles Jarod Wilson <jarod@redhat.com> - 2015-10-24 05:50 +0200
  Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Tom Herbert <tom@herbertland.com> - 2015-10-24 06:50 +0200
  Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-24 08:00 +0200
    Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Michal Kubecek <mkubecek@suse.cz> - 2015-10-26 10:50 +0100
      Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Jarod Wilson <jarod@redhat.com> - 2015-10-30 17:30 +0100
        Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-30 21:10 +0100
          Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Jarod Wilson <jarod@redhat.com> - 2015-11-02 18:40 +0100
    Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Jarod Wilson <jarod@redhat.com> - 2015-10-30 17:40 +0100
      Re: [RFC PATCH net-next] net/core: initial support for stacked dev  feature toggles Alexander Duyck <alexander.duyck@gmail.com> - 2015-10-30 21:20 +0100
  [PATCH net-next] net/core: generic support for disabling netdev features down stack Jarod Wilson <jarod@redhat.com> - 2015-11-02 19:00 +0100
    Re: [PATCH net-next] net/core: generic support for disabling netdev  features down stack Alexander Duyck <alexander.duyck@gmail.com> - 2015-11-02 19:10 +0100
      Re: [PATCH net-next] net/core: generic support for disabling netdev  features down stack Jarod Wilson <jarod@redhat.com> - 2015-11-02 23:00 +0100
    [PATCH v2 net-next] net/core: generic support for disabling netdev features down stack Jarod Wilson <jarod@redhat.com> - 2015-11-03 04:00 +0100
      Re: [PATCH v2 net-next] net/core: generic support for disabling  netdev features down stack David Miller <davem@davemloft.net> - 2015-11-03 05:50 +0100
      Re: [PATCH v2 net-next] net/core: generic support for disabling  netdev features down stack Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2015-11-03 11:10 +0100
        Re: [PATCH v2 net-next] net/core: generic support for disabling  netdev features down stack Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-03 15:00 +0100
          Re: [PATCH v2 net-next] net/core: generic support for disabling netdev  features down stack Jarod Wilson <jarod@redhat.com> - 2015-11-03 15:00 +0100
            Re: [PATCH v2 net-next] net/core: generic support for disabling  netdev features down stack Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2015-11-03 15:10 +0100
              Re: [PATCH v2 net-next] net/core: generic support for disabling netdev  features down stack Jarod Wilson <jarod@redhat.com> - 2015-11-03 17:10 +0100
      [PATCH net-next] net/core: fix for_each_netdev_feature Jarod Wilson <jarod@redhat.com> - 2015-11-03 16:20 +0100
        Re: [PATCH net-next] net/core: fix for_each_netdev_feature Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2015-11-03 16:50 +0100
        Re: [PATCH net-next] net/core: fix for_each_netdev_feature David Miller <davem@davemloft.net> - 2015-11-03 17:40 +0100
      [PATCH net-next] net/core: ensure features get disabled on new lower devs Jarod Wilson <jarod@redhat.com> - 2015-11-03 21:40 +0100
        Re: [PATCH net-next] net/core: ensure features get disabled on new  lower devs Alexander Duyck <alexander.duyck@gmail.com> - 2015-11-03 22:20 +0100
          Re: [PATCH net-next] net/core: ensure features get disabled on new  lower devs Jarod Wilson <jarod@redhat.com> - 2015-11-03 23:20 +0100
            Re: [PATCH net-next] net/core: ensure features get disabled on new  lower devs Alexander Duyck <alexander.duyck@gmail.com> - 2015-11-04 00:10 +0100
        Re: [PATCH net-next] net/core: ensure features get disabled on new  lower devs Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2015-11-03 22:30 +0100
        Re: [PATCH net-next] net/core: ensure features get disabled on new  lower devs Michal Kubecek <mkubecek@suse.cz> - 2015-11-03 23:00 +0100
          Re: [PATCH net-next] net/core: ensure features get disabled on new  lower devs Jarod Wilson <jarod@redhat.com> - 2015-11-03 23:00 +0100
        [PATCH v2 net-next] net/core: ensure features get disabled on new lower devs Jarod Wilson <jarod@redhat.com> - 2015-11-04 05:10 +0100
          Re: [PATCH v2 net-next] net/core: ensure features get disabled on  new lower devs David Miller <davem@davemloft.net> - 2015-11-05 04:00 +0100
            Re: [PATCH v2 net-next] net/core: ensure features get disabled on  new lower devs Florian Fainelli <f.fainelli@gmail.com> - 2015-11-13 01:30 +0100
              Re: [PATCH v2 net-next] net/core: ensure features get disabled on  new lower devs Jiri Pirko <jiri@resnulli.us> - 2015-11-13 11:30 +0100
                Re: [PATCH v2 net-next] net/core: ensure features get disabled on new  lower devs Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2015-11-13 12:00 +0100
                Re: [PATCH v2 net-next] net/core: ensure features get disabled on new  lower devs Laura Abbott <labbott@redhat.com> - 2015-11-13 23:40 +0100

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