update dynamic buffer test (sonic-net#14229)

update dynamic buffer test due to the algorithm calculating headroom is changed
The relevant PR: sonic-net/sonic-swss#3235

Change-Id: I29ad3c4d0b9af0c1357c0890328201c3254cbba2

tests/qos/test_buffer.py

@@ -11,7 +11,7 @@
 from tests.common.utilities import wait_until
 from tests.common.helpers.assertions import pytest_assert, pytest_require
 from tests.common.fixtures.conn_graph_facts import conn_graph_facts         # noqa F401
-from tests.common.mellanox_data import is_mellanox_device
+from tests.common.mellanox_data import is_mellanox_device, get_chip_type
 from tests.common.innovium_data import is_innovium_device
 from tests.common.plugins.loganalyzer.loganalyzer import LogAnalyzer
 from tests.common.utilities import check_qos_db_fv_reference_with_table
@@ -3250,7 +3250,6 @@ def mellanox_calculate_headroom_data(duthost, port_to_test):
 
     speed_of_light = 198000000
     minimal_packet_size = 64
-    cell_occupancy = 0
     worst_case_factor = 0
     propagation_delay = 0
     bytes_on_cable = 0
@@ -3262,7 +3261,7 @@ def mellanox_calculate_headroom_data(duthost, port_to_test):
     pipeline_latency = PIPELINE_LATENCY
 
     if is_8lane:
-        pipeline_latency = PIPELINE_LATENCY * 2 - 1024
+        pipeline_latency = PIPELINE_LATENCY * 2
         speed_overhead = port_mtu
     else:
         speed_overhead = 0
@@ -3272,8 +3271,12 @@ def mellanox_calculate_headroom_data(duthost, port_to_test):
     else:
         worst_case_factor = (2 * CELL_SIZE) / (1 + CELL_SIZE)
 
-    cell_occupancy = (100 - SMALL_PACKET_PERCENTAGE +
-                      SMALL_PACKET_PERCENTAGE * worst_case_factor) / 100
+    worst_case_factor = math.ceil(worst_case_factor)
+
+    small_packet_percentage_by_byte = 100 * minimal_packet_size / (
+            (SMALL_PACKET_PERCENTAGE * minimal_packet_size + (100 - SMALL_PACKET_PERCENTAGE) * LOSSLESS_MTU) / 100)
+    byte_num_in_headroom_per_byte_on_cable = (100 - small_packet_percentage_by_byte
+                                              + small_packet_percentage_by_byte * worst_case_factor) / 100
 
     if gearbox_delay == 0:
         bytes_on_gearbox = 0
@@ -3285,12 +3288,19 @@ def mellanox_calculate_headroom_data(duthost, port_to_test):
     if not use_default_peer_response_time:
         peer_response_time = (float(pause_quanta)) * 512 / (1024 * 8)
     bytes_on_cable = 2 * (float(cable_length)) * port_speed * \
-        1000000000 / speed_of_light / (8 * 1024)
+        1000000000 / speed_of_light / (8 * 1000)
+
+    if get_chip_type(duthost) in ["spectrum4", "spectrum5"]:
+        kb_on_tile = port_speed / 1000 * 120 / 8
+    else:
+        kb_on_tile = 0
+    logging.debug(f"kb_on_tile = {kb_on_tile}")
+
     propagation_delay = port_mtu + bytes_on_cable + 2 * \
-        bytes_on_gearbox + MAC_PHY_DELAY + peer_response_time * 1024
+        bytes_on_gearbox + MAC_PHY_DELAY + peer_response_time * 1024 + kb_on_tile
 
     # Calculate the xoff and xon and then round up at 1024 bytes
-    xoff_value = LOSSLESS_MTU + propagation_delay * cell_occupancy
+    xoff_value = LOSSLESS_MTU + propagation_delay * byte_num_in_headroom_per_byte_on_cable
     xoff_value = math.ceil(xoff_value / 1024) * 1024
     xon_value = pipeline_latency
     xon_value = math.ceil(xon_value / 1024) * 1024