#include <const_mirror_session_opt.h>

Inheritance diagram for ConstMirrorSessionOpt:

Public Member Functions
	ConstMirrorSessionOpt (PhvInfo &phv)

IR::Node *	preorder (IR::BFN::Deparser *dp) override

IR::Node *	preorder (IR::BFN::Digest *dfl) override

IR::Node *	preorder (IR::TempVar *tv) override

Detailed Description

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

SPDX-License-Identifier: Apache-2.0 This pass optimizes the following code pattern: if (ig_intr_md.mirror_type == 0) { mirror.emit<HeaderType>(10w0, { ... });

For Tofino1, mirror_id is 10b and generally expected to allocate to PHV16. However, the hardware is capable of accepting PHV8 as well. When a PHV8 is used, the hardware will automatically duplicate the PHV8 to PHV16 by concatenating the PHV8 with itself.

Therefore, if the mirror_id is constant 0, we can use the B0 container which is reserved for deparse_zero to generate the 10b0 value for mirror_id.

This pass can save PHV resource for the following errata implementation: Due to the errata, the packet cannot be "fully" dropped in the deparser – this will cause serious problems. Therefore, it needs to be dropped just past the deparser, i.e. in that mirror component (mirroring engine). Compiler provides the workaround transparently, without requiring everyone to change the way they drop packets. Compiler synthesizes the code that adds packet mirroring using mirror_type 0, which in turn uses mirror session 0, that is reserved and is programmed by the driver to be invalid. So, if P4 program handles a unicast packet (for example), and set drop_ctl=1, the device will see that it still has to mirror that packet to mirror_type 0 and the packet will proceed to the mirroring component. There, it will be mirrored to session 0 (coming from that variable $tmp3), but since it is invalid, the packet will be dropped and will not go to the TM. As a result, if you want to cancel mirroring, the proper way to do it would be to call invalidate(ig_dprsr_md.mirror_type) and not to set ig_dprsr_md.drop_ctl[2:2]=1.

Member Function Documentation

◆ preorder()

IR::Node * ConstMirrorSessionOpt::preorder ( IR::BFN::Digest * d )

override