There is a bug in SQL Server 2008 that causes PREEMPTIVE_OS_GETPROCADDRESS to include and accumulate the execution time of the extended stored procedure (XPROC). The following is an example showing the increase in the GetProcAddress wait time.
select * from sys.dm_os_wait_stats where wait_type = 'PREEMPTIVE_OS_GETPROCADDRESS' or wait_type = 'MSQL_XP'
exec master..xp_dirtree 'f:\'
select * from sys.dm_os_wait_stats where wait_type = 'PREEMPTIVE_OS_GETPROCADDRESS' or wait_type = 'MSQL_XP'
GetProcAddress is used to load the entrypoint in the DLL (XPROC) and should complete quickly but due to the accumulation bug the wait time is inflated. To get a better idea (ballpark) of how long GetProcAddress really takes you can using the following query.
declare @WaitTime bigint
select @WaitTime = wait_time_ms from sys.dm_os_wait_stats where wait_type = 'MSQL_XP'
select @WaitTime - wait_time_ms from sys.dm_os_wait_stats where wait_type = 'PREEMPTIVE_OS_GETPROCADDRESS'
Bob Dorr - Principal SQL Server Escalation Engineer