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Date:      Sat, 30 Mar 2002 22:49:38 -0800 (PST)
From:      Bruce Evans <bde@FreeBSD.org>
To:        cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject:   cvs commit: src/sys/dev/sio sio.c
Message-ID:  <200203310649.g2V6ncg06578@freefall.freebsd.org>

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bde         2002/03/30 22:49:38 PST

  Modified files:
    sys/dev/sio          sio.c 
  Log:
  Hacks for measuring interrupt latency.  Interrupt latency can be
  measured accurately for periodic interrupts provided the interrupts
  don't need to be serviced very quickly to keep their period almost
  constant.  sio output interrupts have this property (interrupt service
  can be delayed for up to 1 character time without the period changing).
  
  This is non-optional and undocumented so that it can be added and
  removed easily.  It has no significant effect unless it is enabled by
  hacking on a variable using a debugger.  Hardclock and statclock interrupts
  would work even better for this, at least on i386's, provided their
  interrupt handlers are fast (as they are in -current but not in -stable
  or in my version of -current).
  
  Revision  Changes    Path
  1.370     +42 -2     src/sys/dev/sio/sio.c

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