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From: Fabien Thomas <fabient@FreeBSD.org>
Date: Thu, 31 Mar 2011 13:59:47 +0000 (UTC)
To: cvs-src-old@freebsd.org
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Subject: cvs commit: src/sys/kern sched_4bsd.c sched_ule.c
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fabient     2011-03-31 13:59:47 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             sched_4bsd.c sched_ule.c 
  Log:
  SVN rev 220198 on 2011-03-31 13:59:47Z by fabient
  
  Clearing the flag when preempting will let the preempted thread run
  too much time. This can finish in a scheduler deadlock with ping-pong
  between two threads.
  
  One sample of this is:
  - device lapic (to have a preemption point on critical_exit())
  - options DEVICE_POLLING with HZ>1499 (to have lapic freq = hardclock freq)
  - running a cpu intensive task (that does not enter the kernel)
  - only one CPU on SMP or no SMP.
  
  As requested by jhb@ 4BSD have received the same type of fix instead of
  propagating the flag to the new thread.
  
  Reviewed by:    jhb, jeff
  MFC after:      1 month
  
  Revision  Changes    Path
  1.150     +2 -6      src/sys/kern/sched_4bsd.c
  1.291     +2 -1      src/sys/kern/sched_ule.c