Support allocate buffer pool based on ratio (sonic-net#3201)

Support allocate buffer pool size based on percentage of available memory by percentage field in BUFFER_POOL table.
It is used in the dynamic buffer model only and represents the percentage of a buffer pool's size compared to the available memory size.
On Nvidia devices, if the percentage is defined, the buffer pool size is available memory * percentage.

cfgmgr/buffer_pool_mellanox.lua

@@ -417,10 +417,12 @@ local pool_size
 if shp_size then
     accumulative_occupied_buffer = accumulative_occupied_buffer + shp_size
 end
+
+local available_buffer = mmu_size - accumulative_occupied_buffer
 if ingress_pool_count == 1 then
-    pool_size = mmu_size - accumulative_occupied_buffer
+    pool_size = available_buffer
 else
-    pool_size = (mmu_size - accumulative_occupied_buffer) / 2
+    pool_size = available_buffer / 2
 end
 
 if pool_size > ceiling_mmu_size then
@@ -429,12 +431,19 @@ end
 
 local shp_deployed = false
 for i = 1, #pools_need_update, 1 do
+    local percentage = tonumber(redis.call('HGET', pools_need_update[i], 'percentage'))
+    local effective_pool_size
+    if percentage ~= nil and percentage >= 0 then
+        effective_pool_size = available_buffer * percentage / 100
+    else
+        effective_pool_size = pool_size
+    end
     local pool_name = string.match(pools_need_update[i], "BUFFER_POOL|([^%s]+)$")
     if shp_size ~= 0 and pool_name == "ingress_lossless_pool" then
-        table.insert(result, pool_name .. ":" .. math.ceil(pool_size) .. ":" .. math.ceil(shp_size))
+        table.insert(result, pool_name .. ":" .. math.ceil(effective_pool_size) .. ":" .. math.ceil(shp_size))
         shp_deployed = true
     else
-        table.insert(result, pool_name .. ":" .. math.ceil(pool_size))
+        table.insert(result, pool_name .. ":" .. math.ceil(effective_pool_size))
     end
 end
 

tests/test_buffer_dynamic.py

@@ -903,3 +903,34 @@ def test_bufferPoolInitWithSHP(self, dvs, testlog):
             self.config_db.delete_entry('DEFAULT_LOSSLESS_BUFFER_PARAMETER', 'AZURE')
             self.app_db.delete_entry("BUFFER_PG_TABLE_SET", "")
             dvs.runcmd("kill -s SIGCONT {}".format(oa_pid))
+
+
+    def test_bufferPoolPercentage(self, dvs, testlog):
+        self.setup_db(dvs)
+
+        try:
+            self.config_db.delete_field('BUFFER_POOL', 'ingress_lossless_pool', 'size')
+        except Exception as e:
+            pass
+
+        try:
+            percentage = 75
+            margin = 1
+
+            re_pool_size = "ingress_lossless_pool:([0-9]+)"
+            _, original_output = dvs.runcmd("redis-cli --eval /usr/share/swss/buffer_pool_vs.lua")
+            original_size = int(re.match(re_pool_size, original_output).group(1))
+
+            original_ingress_lossless_pool = self.config_db.get_entry('BUFFER_POOL', 'ingress_lossless_pool')
+            ingress_lossless_pool = original_ingress_lossless_pool
+            ingress_lossless_pool['percentage'] = str(percentage)
+            self.config_db.update_entry('BUFFER_POOL', 'ingress_lossless_pool', ingress_lossless_pool)
+
+            _, percentage_output = dvs.runcmd("redis-cli --eval /usr/share/swss/buffer_pool_vs.lua")
+            percentage_size = int(re.match(re_pool_size, percentage_output).group(1))
+
+            real_percentage = percentage_size * 100 / original_size
+            assert abs(percentage - real_percentage) < margin
+        finally:
+            self.config_db.delete_entry('BUFFER_POOL', 'ingress_lossless_pool')
+            self.config_db.update_entry('BUFFER_POOL', 'ingress_lossless_pool', original_ingress_lossless_pool)