[Broadcom-DNX] Pause frames sent for Priority 0 traffic with new MMU buffer settings.

[amitpawar12]

Description

With new MMU buffer settings ( #18239 ), there are Priority 0 PFC frames sent by DUT on congestion.

Steps to reproduce the issue:

1. Apply the new MMU buffer settings. Check the MMU configuration to ensure that buffer settings are applied.

   
   Pool: ingress_lossless_pool
   ----  ----------
   mode  dynamic
   size  6441610000
   type  both
   xoff  396096307
   ----  ----------

Profile: egress_lossless_profile

---

dynamic_th -1 pool ingress_lossless_pool size 0

---

Profile: egress_lossy_profile

---

dynamic_th -1 pool ingress_lossless_pool size 0

---

Profile: ingress_lossy_profile

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dynamic_th -6 pool ingress_lossless_pool size 0 xon_offset 0

---

Profile: pg_lossless_100000_2000m_profile

---

dynamic_th -6 pool ingress_lossless_pool size 0 xoff 393216 xon 2560 xon_offset 363506

---

2. Enable PFCWD and Credit-watchdog on the DUT.
3. Ensure that there are 2 ingress links and 1 egress link of the same link speeds.
4. Send traffic with lossless priorities 3 and 4 and lossy priorities 0, 1 and 2. Select equal ratio of traffic for all 5 priorities (20% in this case) through each of the ingress. One can also have each ingress send let's say 60% of link capacity oversubscribing the egress link.
5. DUT experiences congestion in this case due to oversubscription of the egress link.
6. Check for the PFCs for all the priorities.

Tagging @vmittal-msft for this issue.

#### Describe the results you received:
It is seen that DUT is sending PFCs for Priority 3 and 4 trying to stem the ingress lossless flows. However, it also sends PFCs for lossy priorities via Priority 0 Pause frames.

Received or Transmitted PFC counts ixre-egl-board73_ethernet0_tx_pfc_0 : 442314697 <<<< ixre-egl-board73_ethernet0_tx_pfc_3 : 12588993 ixre-egl-board73_ethernet0_tx_pfc_4 : 12528685 ixre-egl-board73_ethernet8_tx_pfc_0 : 445819671 <<<< ixre-egl-board73_ethernet8_tx_pfc_3 : 12593364 ixre-egl-board73_ethernet8_tx_pfc_4 : 12524065

#### Describe the results you expected:
DUT should have sent PFCs for priority 3 and 4 only.

#### Output of `show version`:

(paste your output here)

#### Output of `show techsupport`:

(paste your output here or download and attach the file here )

#### Additional information you deem important (e.g. issue happens only occasionally):

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     Also attach debug file produced by `sudo generate_dump`
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[amitpawar12]

New MMU buffer settings are available as part of PR #19653. We (nokia team) are working to see if the issue is seen again.

Thanks, -A

[vmittal-msft]

This is fixed with latest MMU settings. Closing the issue.