Wed, Feb 24, 2016 at 09:04:40AM CET, a...@vadai.me wrote:
>On Tue, Feb 23, 2016 at 11:03:21AM -0800, John Fastabend wrote:
>> In the initial implementation the only way to stop a rule from being
>> inserted into the hardware table was via the device feature flag.
>> However this doesn't work well when working on an end host system
>> where packets are expect to hit both the hardware and software
>> datapaths.
>>
>> For example we can imagine a rule that will match an IP address and
>> increment a field. If we install this rule in both hardware and
>> software we may increment the field twice. To date we have only
>> added support for the drop action so we have been able to ignore
>> these cases. But as we extend the action support we will hit this
>> example plus more such cases. Arguably these are not even corner
>> cases in many working systems these cases will be common.
>>
>> To avoid forcing the driver to always abort (i.e. the above example)
>> this patch adds a flag to add a rule in software only. A careful
>> user can use this flag to build software and hardware datapaths
>> that work together. One example we have found particularly useful
>> is to use hardware resources to set the skb->mark on the skb when
>> the match may be expensive to run in software but a mark lookup
>> in a hash table is cheap. The idea here is hardware can do in one
>> lookup what the u32 classifier may need to traverse multiple lists
>> and hash tables to compute. The flag is only passed down on inserts
>> on deletion to avoid stale references in hardware we always try
>> to remove a rule if it exists.
>>
>> Notice we do not add a hardware only case here. If you were to
>> add a hardware only case then you are stuck with the problem
>> of where to stick the software representation of that filter
>> rule. If its stuck on the same filter list as the software only and
>> software/hardware rules it then has to be walked over and ignored
>> in the classify path. The overhead is not huge but is measurable.
>> And with so much work being invested in speeding up rx/tx of
>> pkt processing this is unacceptable IMO. The other option is to
>> have a special hook just for hardware only resources. This is
>> implemented in the next patch.
>>
>> Signed-off-by: John Fastabend <john.r.fastab...@intel.com>
>
>[...]
>
>>
>> -static bool u32_should_offload(struct net_device *dev)
>> +static bool u32_should_offload(struct net_device *dev, u32 flags)
>> {
>> if (!(dev->features & NETIF_F_HW_TC))
>> return false;
>>
>> - return dev->netdev_ops->ndo_setup_tc;
>> + if (flags & TCA_U32_FLAGS_SOFTWARE)
>> + return false;
>> +
>> + if (!dev->netdev_ops->ndo_setup_tc)
>> + return false;
>> +
>> + return true;
>> }
>This function and flag should be a generic filter attribute - not just
>u32.
I agree, this should be generic.
Regarding flags attr, we have the same situation as with other common
attrs:
TCA_U32_POLICE
TCA_FLOW_POLICE
TCA_CGROUP_POLICE
TCA_BPF_POLICE
TCA_U32_ACT
TCA_FLOW_ACT
TCA_CGROUP_ACT
TCA_BPF_ACT
TCA_FLOWER_ACT
I guess we have no other choice then to have
TCA_U32_FLAGS
TCA_FLOWER_FLAGS etc :(
