On 16-02-24 12:40 AM, Jiri Pirko wrote: > Wed, Feb 24, 2016 at 09:04:40AM CET, [email protected] 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 <[email protected]> >> >> [...] >> >>> >>> -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 :( >
Sure if you want to lift it out of u32 I can do that. Seeing there are no other users I planned to do it when I added the next hardware classifier. But sure I can do it now and save a patch later. The flags however likely stays with with TCA_U32_FLAGS until there is some better way to group common attributes in 'tc' framework. .John
