  Benefits of FAST_PATH? 
 The Question is:
 
Without recoding our applications, where can
we expect to see an increase in I/O performance
by setting FAST_PATH to 1?
 
Thanks.
 
 
 The Answer is:
 
  Fast Path may or may not help in a specific situation.  Fast Path does
  provide two distinct benefits:
 
  1) It removes some overhead from disk I/O operations through DUDRIVER to
  CI ports (CIPCA or CIXCD).  This will help you if you are using HSC/HSJ
  controllers.  This translates into a reduction of CPU cost per I/O
  operation.
 
  2) It spreads the I/O load across multiple processors in a multiprocessor
  system, but again only for DUDRIVER and CI ports.  This helps by relieving
  the interrupt processing load on the primary processor, and secondarily by
  taking advantage of caches, by finishing an I/O operation on the processor
  on which it started.  This also translates into a reduction of CPU cost
  per I/O operation.
 
  In addition, fast path helps by reducing the time the IOLOCK8 spinlock is
  held, which can further improve throughput in a multiprocessor system
  (IOLOCK8 is the major bottleneck in parallel I/O operations).
 
  If your environment doesn't use DUDRIVER or CI ports, enabling fast path
  will not help you at all.
 
  The amount of benefit you will see depends on a number of factors, and is
  impossible to quantify without a detailed analysis of your system and
  application load.
 
  If you are able to recode your applications, consider using the $IO_SETUP
  and $IO_PERFORM system services.  These services provide a streamlined way
  to do I/O, and may provide a performance benefit, by reducing the CPU cost
  per I/O operation.  Again, the benefit is impossible to quantify without
  a detailed analysis of your system and application.
 
