Sql Server: Find Long Running Query Or Performace Killing Query

--To Find Long Running Query-----

SELECT TOP 20 SUBSTRING(qt.text, (qs.statement_start_offset/2)+1,

((CASE qs.statement_end_offset

WHEN -1 THEN DATALENGTH(qt.text)

ELSE qs.statement_end_offset

END - qs.statement_start_offset)/2)+1),

qs.execution_count,

qs.total_logical_reads, qs.last_logical_reads,

qs.min_logical_reads, qs.max_logical_reads,

qs.total_elapsed_time, qs.last_elapsed_time,

qs.min_elapsed_time, qs.max_elapsed_time,

qs.last_execution_time,

qp.query_plan

FROM sys.dm_exec_query_stats qs

CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) qt

CROSS APPLY sys.dm_exec_query_plan(qs.plan_handle) qp

WHERE qt.encrypted=0

ORDER BY qs.total_logical_reads DESC