[image_config]: Enable Receive Packet Steering (RPS)

 * This patch enables Receive Packet Steering (RPS) which helps to distribute
   softirq processing for CPU bound packets to all available cores. This will
   help prevent kernel packet drops when there are bouts of intense CPU bound
   packets.

   Ref: https://lwn.net/Articles/362339/
        https://docs.kernel.org/networking/scaling.html

Signed-off-by: Prabhat Aravind <paravind@microsoft.com>

files/build_templates/sonic_debian_extension.j2

@@ -715,6 +715,11 @@ sudo cp $IMAGE_CONFIGS/backend_acl/backend-acl.service $FILESYSTEM_ROOT_USR_LIB_
 sudo cp $IMAGE_CONFIGS/backend_acl/backend_acl.py $FILESYSTEM_ROOT/usr/bin/backend_acl.py
 echo "backend-acl.service" | sudo tee -a $GENERATED_SERVICE_FILE
 
+# Copy RPS script and service file
+sudo cp $IMAGE_CONFIGS/rps/rps.service $FILESYSTEM_ROOT_USR_LIB_SYSTEMD_SYSTEM/rps.service
+sudo cp $IMAGE_CONFIGS/rps/rps.py $FILESYSTEM_ROOT/usr/bin/rps.py
+echo "rps.service" | sudo tee -a $GENERATED_SERVICE_FILE
+
 # Copy SNMP configuration files
 sudo cp $IMAGE_CONFIGS/snmp/snmp.yml $FILESYSTEM_ROOT/etc/sonic/
 

files/image_config/rps/rps.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+import os
+import ast
+import subprocess
+
+'''
+Script to enable Receive Packet Steering (RPS)
+'''
+
+def exec_cmd(cmd):
+    p = subprocess.Popen(cmd, shell=False, executable='/bin/bash',
+                         stdout = subprocess.PIPE)
+    return (p.communicate()[0].strip())
+
+
+def configure_rps():
+    num_cpus = ast.literal_eval(exec_cmd("nproc"))
+    cpumask = hex(pow(2, num_cpus) - 1)[2:]
+    net_dir_path = "/sys/class/net"
+
+    for intf in os.listdir(net_dir_path):
+        if "Ethernet" in intf:
+            queues_path = os.path.join(net_dir_path, intf, "queues")
+            queues = os.listdir(queues_path)
+            num_rx_queues = len([q for q in queues if q.startswith("rx")])
+            for q in range(num_rx_queues):
+                path = os.path.join(queues_path, "rx-{}", "rps_cpus").format(q)
+                command = "echo {} | sudo tee  {}".format(cpumask, path)
+                print ("Setting {} to cpu mask {}".format(path, cpumask))
+                print (command)
+                exec_cmd(command)
+
+
+if __name__ == "__main__":
+    configure_rps()
+

files/image_config/rps/rps.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Enable Receive Packet Steering (RPS) in kernel
+After=swss.service
+BindsTo=sonic.target
+After=sonic.target
+
+[Service]
+User=root
+Type=oneshot
+ExecStart=/usr/bin/rps.py
+RemainAfterExit=yes
+
+[Install]
+WantedBy=sonic.target