doc: describe ACL classification methods

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Siobhan Butler <siobhan.a.butler@intel.com>

diff --git a/doc/guides/prog_guide/packet_classif_access_ctrl.rst b/doc/guides/prog_guide/packet_classif_access_ctrl.rst
index e018c68..d2adbff 100644 (file)
--- a/doc/guides/prog_guide/packet_classif_access_ctrl.rst
+++ b/doc/guides/prog_guide/packet_classif_access_ctrl.rst
@@ -269,6 +269,22 @@ When creating a set of rules, for each rule, additional information must be supp
     When adding new rules into an ACL context, all fields must be in host byte order (LSB).
     When the search is performed for an input tuple, all fields in that tuple must be in network byte order (MSB).
 
+Classification methods
+~~~~~~~~~~~~~~~~~~~~~~
+
+After rte_acl_build() over given ACL context has finished successfully, it can be used to perform classification - search for a ACL rule with highest priority over the input data.
+There are several implementations of classify algorithm:
+
+*   **RTE_ACL_CLASSIFY_SCALAR**: generic implementation, doesn't require any specific HW support.
+
+*   **RTE_ACL_CLASSIFY_SSE**: vector implementation, can process up to 8 flows in parallel. Requires SSE 4.1 support.
+
+*   **RTE_ACL_CLASSIFY_AVX2**: vector implementation, can process up to 16 flows in parallel. Requires AVX2 support.
+
+It is purely a runtime decision which method to choose, there is no build-time difference.
+All implementations operates over the same internal RT structures and use similar principles. The main difference is that vector implementations can manually exploit IA SIMD instructions and process several input data flows in parallel.
+At startup ACL library determines the highest available classify method for the given platform and sets it as default one. Though the user has an ability to override the default classifier function for a given ACL context or perform particular search using non-default classify method. In that case it is user responsibility to make sure that given platform supports selected classify implementation.
+
 Application Programming Interface (API) Usage
 ---------------------------------------------