Experimental Physics and
Industrial Control System

mdavidsaver via Core-talk <core-talk at aps.anl.gov> · Fri, 07 Feb 2020 18:40:57 -0000

Maybe relevant https://bugs.launchpad.net/epics-base/+bug/1861612

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https://bugs.launchpad.net/bugs/541353

Title:
  epicsThreadSleepQuantum() not accurate

Status in EPICS Base:
  Triaged

Bug description:
  epicsThreadSleepQuantum() returns the system clock period on most
  architectures, but on many this is not the actual minimum sleep
  period, as measured by epicsThreadPerform.

  Additional information:
  Suggestion from J. Lewis Muir:

  As a first step, I could see adding a function such as

    void epicsThreadSetSleepQuantum(double quantum);

  If someone knows what the sleep quantum should be for their particular
  machine (by experiment or otherwise), they can set it explicitly (at
  IOC boot time or whenever).  If this function is never called,
  epicsThreadSleepQuantum() behaves just as it does now.  But if
  epicsThreadSetSleepQuantum() has been called,
  epicsThreadSleepQuantum() returns the explicitly set quantum.

  A step beyond this first step might not be a good idea.  But if one
  was to try to implement a step 2 by tackling the problem of
  automatically determining the actual sleep quantum, perhaps a function
  could be added with this signature:

    void epicsThreadCalibrateSleepQuantum(void);

  This function would use an algorithm to determine the actual sleep
  quantum and set it via step 1's epicsThreadSetSleepQuantum().  If the
  user would like to potentially get a more accurate sleep quantum than
  what is reported by epicsThreadSleepQuantum(), he or she could call
  this function (at IOC boot time or whenever).  Again, the default is
  the behavior we have now; the user would have to explicitly call this
  function to get this new behavior.

  What algorithm to use is where things might become difficult.  I could
  see it being difficult to come up with an algorithm that would
  correctly determine a good actual sleep quantum for the wide range of
  hardware and operating systems on which EPICS runs.

  Original Mantis Bug: mantis-324
      http://www.aps.anl.gov/epics/mantis/view_bug_page.php?f_id=324

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System