[Reclaim unused buffer] Support zero buffer profiles

[stephenxs]

Why I did it

Support zero buffer profiles

1. Add buffer profiles and pool definition for zero buffer profiles
2. Support applying zero profiles on INACTIVE PORTS
3. Enable dynamic buffer manager to load zero pools and profiles from a JSON file

Signed-off-by: Stephen Sun stephens@nvidia.com

How I did it

1. Add buffer profiles and pool definition for zero buffer profiles

   • If the buffer model is static:
     • Apply normal buffer profiles to admin-up ports
     • Apply zero buffer profiles to admin-down ports
   • If the buffer model is dynamic:
     • Apply normal buffer profiles to all ports
     • buffer manager will take care when a port is shut down

2. Update buffers_config.j2 to support INACTIVE PORTS by extending the existing macros to generate the various buffer objects, including PGs, queues, ingress/egress profile lists

   • Originally, all the macros to generate the above buffer objects took active ports only as an argument
   • Now that buffer items need to be generated on inactive ports as well, an extra argument representing the inactive ports need to be added
   • To be backward compatible, a new series of macros are introduced to take both active and inactive ports as arguments
   • The original version (with active ports only) will be checked first. If it is not defined, then the extended version will be called
   • Only vendors who support zero profiles need to change their buffer templates

3. Enable buffer manager to load zero pools and profiles from a JSON file:

   • The JSON file is provided on a per-platform basis
   • It is copied from platform/<vendor> folder to /usr/share/sonic/temlates folder in compiling time and rendered when the swss container is being created.

4. To make code clean and reduce redundant code, extract common macros from buffer_defaults_t{0,1}.j2 of all SKUs to two common files:

   • One in Mellanox-SN2700-D48C8 for single ingress pool mode
   • The other in ACS-MSN2700 for double ingress pool mode

   Those files of all other SKUs will be symbol link to the above files

5. Update sonic-cfggen test accordingly:

   • Adjust example output file of JSON template for unit test
   • Add unit test in for Mellanox's new buffer templates.

How to verify it

1. Regression test.
2. Unit test in sonic-cfggen

Run regression test and manually test.

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106

Description for the changelog

A picture of a cute animal (not mandatory but encouraged)