cvs commit: src/sys/amd64/amd64 mp_machdep.c src/sys/i386/i386 mp_machdep.c

Colin Percival cperciva at
Wed Nov 28 15:24:07 PST 2007

cperciva    2007-11-28 23:24:07 UTC

  FreeBSD src repository

  Modified files:        (Branch: RELENG_7)
    sys/amd64/amd64      mp_machdep.c 
    sys/i386/i386        mp_machdep.c 
  Back out previous commit; i.e., turn hyperthreading back on by default.
  Newer Intel processors have better hyperthreading implementations than
  the original ones, and FreeBSD's SMP and scheduler code has greatly
  improved between 6.x and 7.x; so hyperthreading now provides a
  non-trivial performance win.
  Note that security issues involving shared caches and other
  microarchitectural features (e.g., dynamic branch prediction tables)
  still exist; consequently, it is recommended that hyperthreading be
  turned off on systems with untrusted local users.  This can be
  performed by setting machdep.hyperthreading_allowed=0 in
  Hyperthreading will continue to be disabled by default on FreeBSD 6.x.
  Requested by:   core
  Approved by:    re (kensmith)
  Security:       See FreeBSD-SA-05:09.htt for background information.
  Revision   Changes    Path  +1 -1      src/sys/amd64/amd64/mp_machdep.c  +1 -1      src/sys/i386/i386/mp_machdep.c

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