[Fastboot] Delay PMON service for better fastboot performance (#10567)

- Why I did it
Profiling the system state on init after fast-reboot during create_switch function execution, it is possible to see few python scripts running at the same time.
This parallel execution consume CPU time and the duration of create_switch is longer than it should be.
Following this finding, and the motivation to ensure these services will not interfere in the future, PMON is delayed in 90 seconds until the system finish the init flow after fastboot.

- How I did it
Add a timer for PMON service.
Exclude for MLNX platform the start trigger of PMON when SYNCD starts in case of fastboot.
Copy the timer file to the host bin image.

- How to verify it
Run fast-reboot on MLNX platform and observe faster create_switch execution time.

files/build_templates/init_cfg.json.j2

@@ -30,6 +30,7 @@
 {%- set features = [("bgp", "enabled", false, "enabled"),
                    ("database", "always_enabled", false, "always_enabled"),
                    ("lldp", "enabled", true, "enabled"),
+                   ("pmon", "enabled", true, "enabled"),
                    ("pmon", "enabled", false, "enabled"),
                    ("radv", "enabled", false, "enabled"),
                    ("snmp", "enabled", true, "enabled"),

files/build_templates/pmon.service.j2

@@ -17,6 +17,3 @@ ExecStartPre=/usr/bin/{{docker_container_name}}.sh start
 ExecStart=/usr/bin/{{docker_container_name}}.sh wait
 ExecStop=/usr/bin/{{docker_container_name}}.sh stop
 RestartSec=30
-
-[Install]
-WantedBy=sonic.target

files/build_templates/pmon.timer

@@ -0,0 +1,12 @@
+[Unit]
+# This delay is for fast/warm reboot performance
+Description=Delays pmon docker until SONiC has started
+PartOf=pmon.service
+
+[Timer]
+OnUnitActiveSec=0 sec
+OnBootSec=1min 30 sec
+Unit=pmon.service
+
+[Install]
+WantedBy=timers.target sonic.target sonic-delayed.target

files/build_templates/sonic_debian_extension.j2

@@ -831,6 +831,9 @@ sudo cp $BUILD_TEMPLATES/mgmt-framework.timer $FILESYSTEM_ROOT_USR_LIB_SYSTEMD_S
 echo "mgmt-framework.timer" | sudo tee -a $GENERATED_SERVICE_FILE
 {% endif %}
 
+sudo cp $BUILD_TEMPLATES/pmon.timer $FILESYSTEM_ROOT_USR_LIB_SYSTEMD_SYSTEM
+echo "pmon.timer" | sudo tee -a $GENERATED_SERVICE_FILE
+
 sudo cp $BUILD_TEMPLATES/sonic.target $FILESYSTEM_ROOT_USR_LIB_SYSTEMD_SYSTEM
 sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable sonic.target
 

files/scripts/syncd.sh

@@ -45,10 +45,15 @@ function startplatform() {
 
 function waitplatform() {
 
+    BOOT_TYPE=`getBootType`
     if [[ x"$sonic_asic_platform" == x"mellanox" ]]; then
-        debug "Starting pmon service..."
-        /bin/systemctl start pmon
-        debug "Started pmon service"
+        if [[ x"$BOOT_TYPE" = @(x"fast"|x"warm"|x"fastfast") ]]; then
+            debug "PMON service is delayed by a timer for better fast/warm boot performance"
+        else
+            debug "Starting pmon service..."
+            /bin/systemctl start pmon
+            debug "Started pmon service"
+        fi
     fi
     if [[ x"$BOOT_TYPE" = @(x"fast"|x"warm"|x"fastfast") ]]; then
         debug "LLDP service is delayed by a timer for better fast/warm boot performance"