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Disabling Hyper-Threading

785 Views 3 Replies Latest reply: May 7, 2012 4:38 AM by Retired Engineer RSS
dontb3trlp3n Calculating status...
Currently Being Moderated
May 7, 2012 3:53 AM

I have a 15" macbook pro(late 2011 2.4ghz) with lion 10.7.3 and would like to turn off Hyper-Threading to decrease my Encode Times. Handbreak only uses 600% of the cpu instead of 800%. I tried to diable it using the command "sudo nvram SMT=0" when i check it after restarting, it says smt is "0" but all Logical Cores are still active.


Is Anybody else have the same issue or am i doing something wrong?

MacBook Pro, Mac OS X (10.7.3)
  • Retired Engineer Level 4 Level 4 (2,710 points)
    Currently Being Moderated
    May 7, 2012 4:17 AM (in response to dontb3trlp3n)

    Turning off hyperthreading will not decrease your encoding times, it will increase them.

    You don't say what cpu you have but disabling hyperthreading would cut it's capability in half.

  • Retired Engineer Level 4 Level 4 (2,710 points)
    Currently Being Moderated
    May 7, 2012 4:38 AM (in response to dontb3trlp3n)

    That processor has 4 cores.  Hyperthreading lets it handle 8 threads at the same time.  The hyperthreading hardware provides an extra set of registers for each core.  Switching between register sets is extremely fast.

    The net effect is only slightly slower than an 8 core non-hyperthreaded processor.


    How many threads the program you are running can use was determined by the author of the program.  If it was written as a single threaded program it will never use more than one thread on the processor.


    If it was written to use 8 threads (highly unlikely) and you disable hyperthreading it would take twice as long to run.


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