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From: Luigi Rizzo <luigi@FreeBSD.org>
Date: Mon, 14 Feb 2011 08:09:02 +0000 (UTC)
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Subject: cvs commit: src/sys/geom/sched gs_rr.c
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luigi       2011-02-14 08:09:02 UTC

  FreeBSD src repository

  Modified files:
    sys/geom/sched       gs_rr.c 
  Log:
  SVN rev 218675 on 2011-02-14 08:09:02Z by luigi
  
  Correct a subtle bug in the 'gsched_rr' disk scheduler.
  The algorithm is supposed to work as follows:
  in order to prevent starvation, when a new client starts being served we
  record the start time and reset the counter of bytes served.
  We then switch to a new client after a certain amount of time or bytes,
  even if the current one still has pending requests.
  To avoid charging a new client the time of the first seek,
  we start counting time when the first request is served.
  
  Unfortunately a bug in the previous version of the code failed
  to set the start time in certain cases, resulting in some processes
  exceeding their timeslice.
  
  The fix (in this patch) is trivial, though it took a while to find
  out and replicate the bug.
  Thanks to Tommaso Caprai for investigating and fixing the problem.
  
  Submitted by:   Tommaso Caprai
  MFC after:      1 week
  
  Revision  Changes    Path
  1.4       +20 -8     src/sys/geom/sched/gs_rr.c