Torino is a AMD Athlon XP 2600+ running Linux 2.6.7 and Sun's JDK 1.4.2.

NullAppender:

    4.67 PatternLayout "%p - %m%n"
    4.67 PatternLayout "%-5p - %m%n"
   11.22 PatternLayout "%r [%t] %-5p %c{2} %x - %m%n"
   11.34 PatternLayout "%r [%t] %-5p %.10c %x - %m%n"
   11.30 PatternLayout "%r [%t] %-5p %.20c %x - %m%n"
   10.04 PatternLayout "%r [%t] %-5p %c - %m%n"
   18.21 PatternLayout "%d{ISO8601} [%t] %-5p %c %x - %m%n"
   18.11 PatternLayout "%d{yyyy-MM-dd HH:mm:ss,SSS} [%t] %-5p %c %x - %m%n"
  183.81 PatternLayout "%l - %m%n"
  203.25 PatternLayout "%C.%M.%L - %m%n"

FileAppender:

   15.11 PatternLayout "%p - %m%n"					   
   16.96 PatternLayout "%-5p - %m%n"					   
   24.60 PatternLayout "%r [%t] %-5p %c{2} %x - %m%n"			   
   24.37 PatternLayout "%r [%t] %-5p %.10c %x - %m%n"			   
   25.72 PatternLayout "%r [%t] %-5p %.20c %x - %m%n"			   
   23.09 PatternLayout "%r [%t] %-5p %c - %m%n"				   
   35.80 PatternLayout "%d{ISO8601} [%t] %-5p %c %x - %m%n"		   
   36.26 PatternLayout "%d{yyyy-MM-dd HH:mm:ss,SSS} [%t] %-5p %c %x - %m%n"
  243.57 PatternLayout "%l - %m%n"					   
  258.75 PatternLayout "%C.%M.%L - %m%n"                                     

FileAppender: (ImmediateFlush=false)

   6.96 PatternLayout "%p - %m%n"					   
   7.07	PatternLayout "%-5p - %m%n"					   
  15.33	PatternLayout "%r [%t] %-5p %c{2} %x - %m%n"			   
  15.18	PatternLayout "%r [%t] %-5p %.10c %x - %m%n"			   
  16.49	PatternLayout "%r [%t] %-5p %.20c %x - %m%n"			   
  14.21	PatternLayout "%r [%t] %-5p %c - %m%n"				   
  23.33	PatternLayout "%d{ISO8601} [%t] %-5p %c %x - %m%n"		   
  23.13	PatternLayout "%d{yyyy-MM-dd HH:mm:ss,SSS} [%t] %-5p %c %x - %m%n"
 241.42	PatternLayout "%l - %m%n"					   
 260.15	PatternLayout "%C.%M.%L - %m%n"                                   

FileAppender: (BufferedIO=true)

   6.27 PatternLayout "%p - %m%n"					  
   6.39	PatternLayout "%-5p - %m%n"					  
  15.45	PatternLayout "%r [%t] %-5p %c{2} %x - %m%n"			  
  13.97	PatternLayout "%r [%t] %-5p %.10c %x - %m%n"			  
  14.40	PatternLayout "%r [%t] %-5p %.20c %x - %m%n"			  
  13.10	PatternLayout "%r [%t] %-5p %c - %m%n"				  
  21.78	PatternLayout "%d{ISO8601} [%t] %-5p %c %x - %m%n"		  
  21.64	PatternLayout "%d{yyyy-MM-dd HH:mm:ss,SSS} [%t] %-5p %c %x - %m%n"
 214.99	PatternLayout "%l - %m%n"					  
 239.34	PatternLayout "%C.%M.%L - %m%n"                                    

Notice the small but noticable performance gain when
ImmediateFlush=false

Note also that BufferedIO yeilds better performance than
ImmediateFlush only when the length of the log entry is relatively
long.