Template Netronome P4

A template repository to work with P4 programs on Netronome SmartNICs. Mostly a wrapper around nfp4build with sensible defaults for Agilio CX 2x10GbE SmartNICs.

Usage

This assumes you have the SDK Hosted Toolchain installed locally

1. Click in Use this Template > Create a new repository to create your own repository

2. Clone your repository

3. Run ./configure.sh with the intended options to generate the Makefile

   • Example:

     ./configure.sh --program=my_program --option_n=value --flag_option
     

   • Default options are recommended. See Configuration Options for a full list.

4. Add your program's source files to the src directory

5. Run make to compile your program

6. Load your program:

   make load REMOTEHOST=<target host> CONFIG=<config_file.p4cfg>
   

   • CONFIG default value is configs/config.p4cfg

Note

This will recompile the program applying cache bypass fixes. See Cache Bypass for a full explanation. For just deploying without recompilation use:

make push REMOTEHOST=<target host> CONFIG=<config_file.p4cfg>

7. You can repeat step 3. any time to adjust options and generate a new Makefile

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Critical Sections

Netronome's compiler ignores the @atomic annotation present in P4's specification. To create critical sections an example C plugin is included at src/critical.c.

Usage:

Warning

This implementation utilizes only one spin lock! If you have multiple critical regions they will all share the same lock!

1. Declare the C plugin source file when running the configure.sh script:

   ./configure.sh --sandbox-c=src/critical.c
   

2. Declare the extern functions in P4:

   extern void critical_begin();
   extern void critical_end();

3. Delimit your critical sections:

   critical_begin();
   // Your critical code
   critical_end();

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Cache Bypass

Due to cached lookups in Netronome's P4 implementation, P4 register accesses that affect control flow can result in unexpected behavior. To mitigate this, the pragma @pragma netro no_lookup_caching <action name> can be attached to an action definition forcing the cached lookup to be ignored. Refer to Netronome's documentation for more details.

As of the most recent SDK version, Netronome's compiler fails to compile when such pragma is declared in P4-16 programs. Using #pragma netro no_lookup_caching <action name>, as seen in other public available examples, allows for successful compilation. However, in this case, the pragma is ignored, resulting in no changes to the final program.

The scripts at utils/ provide a workaround to this problem by directly adding to the intermediate C generated code the required changes. Using #pragma netro no_lookup_caching <action name> will then result in the expected behavior.

Note

The scripts are executed automatically when running make to compile the program. No manually intervention is required!

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Reglocked

The pragma @pragma netro reglocked <register name> can be used to ensure mutual exclusion when accessing a given register. Refer to Netronome's documentation for more details.

In a similar way to Cache Bypass this does not work with P4-16 and the most recent SDK version!!

Warning

This fix is yet NOT IMPLEMENTED in this template!!

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Configuration Options

Note

nfp4build has additional options available not covered/wrapped by this script but that can also be used. For more details run nfp4build --help.

Option	Description	Default Vaue
--program	Program's name	program
--source	Path to main P4 source file	src/main.p4
--sku	SKU	AMDA0096-0001:0
--platform	Platform	lithium
--me-count	Number of Microengines to instantiate	" " (Maximum)
--sandbox-c	Path to C plugin source file	" " (none)
--no-reduce-threads	Use 8-context mode for microengines	false
--no-shared-codestore	Build with no shared codestore support	false
--disable-flowcache	Disable flow cache	false
--p4-version	P4 version	16
--no-header-ops	Do not allow all headers to be addable/removable	false
--implicit-header-valid	Enable P4 implicit header valid matching semantics	false
--no-zero-new-headers	No strict P4 behaviour of zeroing all new headers	false
--m-group-count	Number of multicast groups to support	16
--m-group-size	Number of multicast ports per group	16