Once you have identified a CPU bottleneck, use sys.dm_os_wait_stats dynamic management view (DMV) to identify the top ten worst-performing queries for the CPU, as shown below.

-- Hardware performance bottlenecks
--
-- Memory
--
-- Memory affects SQL Server performance more than any other piece of hardware.
-- Therefore, it is necessary to monitor memory usage regularly on SQL Server
-- systems to ensure that the percentage of memory available is higher than 20%.
-- If users are experiencing performance issues and the percentage of available
-- memory drops below 20%, then the problem is insufficient memory allocation.
-- Keep an eye on the average page life expectancy performance counter and make
-- sure it is always above 300 seconds (5 minutes). Anything less indicates
-- either poor index design leading to increased disk input/output (I/O) and
-- less effective use of memory or an actual shortage of memory. Monitor the
-- paging rates on the SQL Server system, and make sure they are regularly above
-- 1,000 pages per second. Check the PerfMon object MSSQL Buffer Manager and the
-- Memory Performance Counters.
--
-- Also, monitor the counter, Memory Grants Pending in PerfMon object SQL Server
-- Memory Manager Counters. This counter indicates the total number of processes
-- per second waiting for a workspace memory grant. Typically, small OLTP
-- transactions do not require large memory grants. Anything greater than a
-- memory grant of zero for an OLTP transaction indicates low memory in a SQL
-- Server system.

-- One way to handle memory bottlenecks is to find memory-intensive processes,
-- which can be used to identify potential application problems such as memory
-- leaks. You can also review queries to optimize performance to consume less
-- memory. Another approach is to scale up the SQL Server environment by adding
-- more physical memory (RAM) to the SQL Server. Scaling up is usually a good
-- approach to address any performance bottleneck related to memory.
--
-- Disk I/O use
--
-- Compared to other hardware resources, storage input/output is usually the
-- slowest of the system resources in SQL Server. Therefore, it is important to
-- monitor the storage system to see if storage has become a performance
-- bottleneck. If it has, the next step is to investigate whether or not you can
-- optimize the design and configuration of the storage system to achieve
-- scalability and high performance. Review the PerfMon disk counters for
-- Average Disk Sec/Read and Average Disk Sec/Write. Make sure that the time a
-- read or write takes is, ideally, less than 12 milliseconds for OLTP systems
-- and higher for decision support systems.
--
-- As with memory, the easiest way to solve a disk I/O performance bottleneck is
-- to scale up the SQL Server environment by replacing existing disks with
-- faster disks that can better cope with the I/O load and that distribute the
-- I/O load across multiple spindles. Also, defragment the data disk regularly.
--
-- CPU
--
-- CPU performance bottlenecks occur for a variety of reasons. They include
-- having a non-optimal query plan, an inadequate design application or database
-- design, poor SQL Server configuration or a lack of hardware resources. Review
-- the PerfMon operation system CPU and processor counters for Processor Queue
-- Length to verify that the number of threads waiting for CPU cycles is eight
-- or less. If this number is greater than 12, it means that the CPU is causing
-- the performance issue.
--
-- Once you have identified a CPU bottleneck, use sys.dm_os_wait_stats dynamic
-- management view (DMV) to identify the top ten worst-performing queries for
-- the CPU, as shown below.
--
-- http://searchsqlserver.techtarget.com/tip/Five-tips-to-avoid-a-performance-bottleneck-or-other-SQL-Server-snares
--

-- To identify the top ten worst-performing queries for the CPU:
select top 10
    (a.total_worker_time / a.execution_count) as [Avg_CPU_Time],
    Convert(varchar, Last_Execution_Time) as [Last_Execution_Time],
    Total_Physical_Reads,
    SUBSTRING(b.text, a.statement_start_offset / 2, (
            case
                when a.statement_end_offset = - 1
                    then len(convert(nvarchar(max), b.text)) * 2
                else a.statement_end_offset
                end - a.statement_start_offset
            ) / 2) as [Query_Text],
    dbname = Upper(db_name(b.dbid)),
    b.objectid as 'Object_ID',
    B.*
from sys.dm_exec_query_stats a
cross apply sys.dm_exec_sql_text(a.sql_handle) as b
order by [Avg_CPU_Time] desc;