On 18 February 2016 at 08:54, Balasubramanian Manoharan < bala.manoha...@linaro.org> wrote:
> Adds user-guide documentation for classification module > > Signed-off-by: Balasubramanian Manoharan <bala.manoha...@linaro.org> > --- > v2: Incorporates review comments from Christophe > > doc/users-guide/users-guide-cls.adoc | 220 > +++++++++++++++++++++++++++++++++++ > 1 file changed, 220 insertions(+) > create mode 100644 doc/users-guide/users-guide-cls.adoc > > diff --git a/doc/users-guide/users-guide-cls.adoc > b/doc/users-guide/users-guide-cls.adoc > new file mode 100644 > index 0000000..74cdcaa > --- /dev/null > +++ b/doc/users-guide/users-guide-cls.adoc > @@ -0,0 +1,220 @@ > +== Classification \(CLS) > I am not sure whether the backslash here is intentionnal or not. It shows up in the final html doc. > + > +ODP is a framework for software-based packet forwarding/filtering > applications, > +and the purpose of the Packet Classification API is to enable > applications to > +program the platform hardware or software implementation to assist in > +prioritization, classification and scheduling of each packet, so that the > +software application can run faster, scale better and adhere to QoS > +requirements. > + > +The following API abstraction are not modelled after any existing product > +implementation, but is instead defined in terms of what a typical > data-plane > +application may require from such a platform, without sacrificing > simplicity and > +avoiding ambiguity. Certain terms that are being used within the context > of > +existing products in relation to packet parsing and classification, such > as > +access lists are avoided such that not to suggest any relationship > +between the abstraction used within this API and any particular manner in > which > +they may be implemented in hardware. > + > +=== Functional Description > + > +Following is the functionality that is required of the classification > API, and > +its underlying implementation. The details and order of the following > paragraph > +is informative, and is only intended to help convey the functional scope > of a > +classifier and provide context for the API. In reality, implementations > may > +execute many of these steps concurrently, or in different order while > +maintaining the evident dependencies: > + > +1. Apply a set of classification rules to the header of an incoming > packet, > +identify the header fields, e.g. ,ethertype, IP version, IP protocol, > transport > +layer port numbers, IP DiffServ, VLAN id, 802.1p priority. > + > +2. Store these fields as packet meta data for application use, and for the > +remainder of parser operations. The odp_pktio is also stored as one of > the meta > +data fields for subsequent use. > + > +3. Compute an odp_cos (Class of Service) value from a subset of supported > fields > +from 1) above. > + > +4. Based on the odp_cos from 3) above, select the odp_queue through which > the > +packet is delivered to the application. > + > +5. Validate the packet data integrity (checksums, FCS) and correctness > (e.g., > +length fields) and store the validation result, along with optional error > layer > +and type indicator, in packet meta data. Optionally, if a packet fails > +validation, override the odp_cos selection in step 3 to a class of service > +designated for errored packets. > + > +6. Based on the odp_cos from 3) above, select the odp_buffer_pool that > should be > +used to acquire a buffer to store the packet data and meta data. > + > +7. Allocate a buffer from odp_buffer_pool selected in 6) above and > logically[1] > +store the packet data and meta data to the allocated buffer, or in > accordance > +with class-of-service drop policy and subject to pool buffer availability, > +optionally discard the packet. > + > +8. Enqueue the buffer into the odp_queue selected in 4) above. > + > +The above is an abstract description of the classifier functionality, and > may be > +applied to a variety of applications in many different ways. The ultimate > +meaning of how this functionality applies to an application also depends > on > +other ODP modules, so the above may not complete a full depiction. For > instance, > +the exact meaning of priority, which is a per-queue attribute is > influenced by > +the ODP scheduler semantics, and the system behavior under stress depends > on the > +ODP buffer pool module behavior. > + > +For the sole purpose of illustrating the above abstract functionality, > here is > +an example of a Layer-2 (IEEE 802.1D) bridge application: Such a > forwarding > +application that also adheres to IEEE 802.1p/q priority, which has 8 > traffic > +priority levels, might create 8 odp_buffer_pool instances, one for each > PCP > +priority level, and 8 odp_queue instances one per priority level. Incoming > +packets will be inspected for a VLAN header; the PCP field will be > extracted, > +and used to select both the pool and the queue. Because each queue will be > +assigned a priority value, the packets with highest PCP values will be > scheduled > +before any packet with a lower PCP value. Also, in a case of congestion, > buffer > +pools for lower priority packets will be depleted earlier than the pools > +containing packets of the high priority, and hence the lower priority > packets > +will be dropped (assuming that is the only flow control method that is > supported > +in the platform) while higher priority packets will continue to be > received into > +buffers and processed. > + > +=== Class of Service Creation and Binding > + > +To program the classifier, a class-of-service instance must be created, > which > +will contain the packet filtering resources that it may require. All > subsequent > +calls refer to one or more of these resources. > + > +Each class of service instance must be associated with a single queue or > queue > +group, which will be the destination of all packets matching that > particular > +filter. The queue assignment is implemented as a separate function call > such > +that the queue may be modified at any time, without tearing down the > filters > +that define the class of service. In other words, it is possible to > change the > +destination queue for a class of service defined by its filters quickly > and > +dynamically. > + > +Optionally, on platforms that support multiple packet buffer pools, each > class > +of service may be assigned a different pool such that when buffers are > exhausted > +for one class of service, other classes are not negatively impacted and > continue > +to be processed. > + > +=== Default packet handling > + > +There is a odp_cos_t assigned to each port with the > odp_pktio_default_cos_set() > +function, which will function as the default class-of-service for all > packets > +received from an ingress port, that do not match any of the filters > defined > +subsequently. At minimum this default class-of-service must have a queue > and a > +buffer pool assigned to it on platforms that support multiple packet > buffer > +pools. Multiple odp_pktio instances (i.e., multiple ports) may each have > their > +own default odp_cos, or may share a odp_cos with other ports, based on > +application requirements. > + > +Packet Classification > + > +For each odp_pktio port, the API allows the assignment of a > class-of-service to > +a packet using one of three methods: > + > +1. The packet may be assigned a specific class-of-service based on its > Layer-2 > +(802.1P/902.1Q VLAN tag) priority field. Since the standard field defines > 8 > +discrete priority levels, the API allows to assign an odp_cos to each of > these > +priority levels with the odp_cos_with_l2_priority() function. > + > +2. Similarly, a class-of-service may be assigned using the Layer-3 (IP > DiffServ) > +header field. The application supplies an array of odp_cos values that > covers > +the entire range of the standard protocol header field, where array > elements do > +not need to contain unique values. There is also a need to specify if > Layer-3 > +priority takes precedence over Layer-2 priority in a packet with both > headers > +present. > + > +3. Additionally, the application may also program a number of pattern > matching > +rules that assign a class-of-service for packets with header fields > matching > +specified values. The field-matching rules take precedence over the > previously > +described priority-based assignment of a class-of-service. Using these > matching > +rules the application should be able for example to identify all packets > +containing VoIP traffic based on the protocol being UDP, and a specific > +destination or source port numbers, and appropriately assign these > packets an > +class-of-service that maps to a higher priority queue, assuring voice > packets a > +lower and bound latency. > + > +Packet meta data Elements > + > +Here are the specific information elements that are stored within the > +packet meta data structure: > + > +* Protocol fields that are decoded and extracted by the parsing phase > + > +* The pool identifier that is selected for the packet > + > +* The ingress port identifier > + > +* The result of packet validation, including an indication of the type of > error > +* detected, if any > + > +The ODP packet API module provides accessors for retrieving the above meta > +data fields from the container buffer in an implementation-independent > manner. > + > +=== Example configuration > + > +CoS configuration can be best illustrated by drawing a tree, where each > CoS is > +the vertex, and each link between any two vertices is a PMR. The root > node for > +the tree is the default CoS which is attached with the pktio interface. > All of > +the CoS vertices can be final for some packets, if these packets do not > match > +any of the links. > + > +Let us consider the below configuration > + > +odp_pktio_default_cos_set(odp_pktio_t pktio, odp_cos_t default_cos); > + > +pmr1 = odp_cls_pmr_create(pmr_match1, default_cos, cos1); > +pmr2 = odp_cls_pmr_create(pmr_match2, default_cos, cos2); > +pmr3 = odp_cls_pmr_create(pmr_match3, default_cos, cos3); > + > +pmr11 = odp_cls_pmr_create(pmr_match11, cos1, cos11); > +pmr12 = odp_cls_pmr_create(pmr_match12, cos1, cos12); > + > +pmr21 = odp_cls_pmr_create(pmr_match11, cos2, cos21); > +pmr31 = odp_cls_pmr_create(pmr_match11, cos3, cos31); > + > +The above configuration DOES imply order - a packet that matches > pmr_match1 will > +then be applied to pmr_match11 and pmr_match12, and as a result could > terminate > +with either cost1, cos11, cos12. In this case the packet was subjected to > two > +match attempts in total. > + > +The remaining two lines illustrate how a packet that matches pmr_match11 > could > +end up wth either cos11, cos21 or cos31, depending on wether it matches > +pmr_march1, pmr_march2 or pmr_match3. > + > +Here is a practical example: > + > +Let's look at DNS packets, these are identified by using UDP port 53, but > each > +UDP packet may run atop of IPv4 or IPv6, and in turn an IP packet might be > +received as either multicast or unicast, > + > +Very simply, we can create these PMRs: > + > +PMR-L2 = match all multicast/broadcast packets based on DMAC address > PMR_L3_IP4 > += match all IPv4 packets PMR_L3_IP6 = match all IPv6 packets PMR_L4_UDP = > match > +all UDP packets PMR_L4_53 = match all packets with dest port = 53. > + > +odp_cls_pmr_create(PMR_L2, default_cos, default_cos_mc); > +odp_cls_pmr_create(PMR_L3_IP4, default_cos, default_cos_ip4_uc); > +odp_cls_pmr_create(PMR_L3_IP6, default_cos, default_cos_ip6_uc); > + > +odp_cls_pmr_create(PMR_L3_IP4, default_cos_mc, default_cos_ip4_mc); > +odp_cls_pmr_create(PMR_L3_IP6, default_cos_mc, default_cos_ip6_mc); > +odp_cls_pmr_create(PMR_L4_UDP, default_cos_ip4_uc, cos_udp4_uc); > +odp_cls_pmr_create(PMR_L4_UDP, default_cos_ip4_mc, cos_udp4_mc); > +odp_cls_pmr_create(PMR_L4_UDP, default_cos_ip6_uc, cos_udp6_uc); > +odp_cls_pmr_create(PMR_L4_UDP, default_cos_ip6_mc, cos_udp6_mc); > + > +odp_cls_pmr_create(PMR_L4_53, cos_udp4_uc, dns4_uc); > +odp_cls_pmr_create(PMR_L4_53, cos_udp4_mc, dns4_mc); > +odp_cls_pmr_create(PMR_L4_53, cos_udp6_uc, dns6_uc); > +odp_cls_pmr_create(PMR_L4_53, cos_udp6_mc, dns6_mc); > + > +In this case, a packet may change CoS between 0 and 5 times, meaning that > up to > +5 PMRs may be applied in series, and the order > + > +Another interesting point is that an implementation will probably impose > on a > +limit of how many PMRs can be applied to a packet in series, so in the > above > +example, if an implementation limit on the number of consecutive > classification > +steps is 4, then all the DNS packets may only reach cos_udp?_?c set of > vertices. > -- > 1.9.1 > > I am fine with this document. but shouldn't be included by the main user guide? Practical examples would be nice, but can be part of a later update I guess. Christophe.
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