Login report of Sysadmin We have got a requirement to provide login report from SQL Server for Sysadmin only - This would have log-in date and time when anyone logged into SQL server having sysadmin privilege.

Is there anyway we can get report from SQL server with details of log-ins of only those users who are Sysadmins on the database server.

I guess, in security tab we can enable both Success and Failed Logins however enabling this would add lot of overhead on server, currently we have enabled this only for failed logins. And I don't know if there is anyway to enable success login only for sysadmin and not for others.

Any help would be appreciated.
You should write a logon trigger that will log only sysadmins.
Here you can find more about logon triggers: 
Logon Triggers

And here is a practical example of its use:
SQL Server – Login Auditing using Logon Triggers

P.S. To find out if the login is a sysadmin you can use this code: 

select is_srvrolemember ('sysadmin',original_login())

UPDATE

If the logon trigger does not use EXECUTE AS clause (and in case of OP this is true), it's executed under the current login. So to check out if the login is sysadmin is sufficient execute

select IS_SRVROLEMEMBER('sysadmin');


without using original_login(). This will work even in case when the AD group is sysadmin, and Windows login is not sysadmin directly but access the server through membership in this AD group