Hi Vignesh. This is a tricky one, in my opinion. In larger enterprise environments, the IT department typically has monitoring systems that track performance and resource utilization on all the servers in the environment. Smaller shops tend not to have those resources, so the approach Matthew provided above will be helpful from a host monitoring perspective.
For us, we've had several monitoring systems set up, but we're currently using Zabbix for our main monitoring system of our Tableau Server instances. We check for CPU utilization and load, free memory, disk space, disk performance, host up/down, and we even have one custom check that pulls the XML from http://server/admin/systeminfo and alerts us is processes are down. The other nice thing about Zabbix is that it provides a means for you to access the underlying database--which means that if the admin opens it up for you, you can pull your performance info into Tableau dashboards! Very convenient. Another future check we're working on is a Zabbix check that tests viz load times for a specific set of popular dashboards.
There is additional performance information that can be found in the Tableau Server PostreSQL repository, but I haven't been able to use it effectively yet to get to the performance data that is really important to me--viz load times. Nevertheless, I do have custom admin views I've built that help me see all extract durations, failures, and successes at a glance, and how late subscriptions are being sent relative to when they were scheduled. You could probably also get a sense of the wait time for non-viz HTTP requests, such as loading a list of Views or Workbooks, which would help monitor the user experience.
In the future we also hope to start capturing log data with Splunk and using that for additional monitoring. Not quite there yet, though.
+1 On Matthew's suggestion, although I'd use the reports he's suggesting to establish a historical baseline for the render time of all your "important" reports. As time goes on and load increases on your server, see if these same reports take about the same amount of time or longer than your historical baseline.
I double Matt here. Zabbix is indeed a great tool for enterprise monitoring and Tableau fits in it perfectly. You can check out my Blog and the Tableau Zabbix Template which you can use as starter to monitor your Tableau environment.