SQL存储过程执行时间之谜

我试图弄明白为什么SQL Server存储过程执行缓慢,所以我引入了一些粗糙的计时器,如:

Create Procedure DoStuff
As Begin

    Declare @Stopwatch datetime 
    Set @Stopwatch=GetDate()

    Print char(13) + 'Task A'
    /* Perform Task A */
    Print DateDiff(ms, @Stopwatch, GetDate()); Set @Stopwatch = GetDate()

    Print char(13) + 'Task B'
    /* Perform Task B */
    Print DateDiff(ms, @Stopwatch, GetDate()); Set @Stopwatch = GetDate()

    Print char(13) + 'Task C'
    -- Perform Task C
    Print DateDiff(ms, @Stopwatch, GetDate()); Set @Stopwatch = GetDate()

End

Exec DoStuff

我得到这样的东西:

Task A
0

Task B
80

Task C
100

所以我认为执行这个过程需要180毫秒。但是,该过程需要3000多毫秒才能执行;在客户机统计信息中,我得到

Client processing time: 12
Total execution time: 3105
Wait time on server replies: 3093

额外2800毫秒的原因是什么?