Magento profiler can help you with the store performance tuning before the store release or during the exploitation.
The old UI for enabling/disabling the profiler is not available in Magento 2 and the profiler is disabled by default.
To enable one of the profiler formats mentioned above, you can edit .htaccess (a configuration file for Apache Web Server software):
Choose one of the next expressions:
1. SetEnv MAGE_PROFILER "html" outputs in the footer of a web store page opened in a browser.
¡To enable the HTML profiler, you can also edit index.php with the next expression: $_SERVER["MAGE_PROFILER"]="html"!
2. SetEnv MAGE_PROFILER "csvfile" outputs into var/log/profiler.csv.
3. SetEnv MAGE_PROFILER "firebug" outputs into var/log/profiler.csv.
Put your website into the developer mode;
Clear the Magento 2 cache.