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vexatious Tux's lil' helper

Joined: 24 Aug 2010 Posts: 77
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Posted: Wed Jun 19, 2013 12:13 am Post subject: Piledriver faster with no SMT-HT scheduler; only MT? |
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Recompiled 3.8.3 kernel without SMT scheduler (smt (hyperthreading) scheduler). Only enabled "multi-core scheduler support" and system seems a little faster (automatic group scheduling enabled). Tried same setting without automatic group scheduling, but normal desktop use seemed somewhat slower; didn't try single application performance however. Wasn't able to test with both scheduler's off (xorg startup issue after re-installing kernel=what the heck? Happened when I reverted back settings too).
Deadline I/O scheduler was always enabled.
Can others with piledriver (maybe bulldozer) confirm this?
Regards _________________ Gentoo
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DONAHUE Watchman


Joined: 09 Dec 2006 Posts: 7550 Location: Goose Creek SC
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Posted: Wed Jun 19, 2013 10:55 pm Post subject: |
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Help for what I assume is the configuration choice you are discussing says: Quote: | SMT (Hyperthreading) scheduler support
│ CONFIG_SCHED_SMT:
│
│ SMT scheduler support improves the CPU scheduler's decision making
│ when dealing with Intel Pentium 4 chips with HyperThreading at a
│ cost of slightly increased overhead in some places. If unsure say
│ N here. | this choice is not applicable for AMD cpus, might introduce a some amount of overhead if that fact has to be repeatedly determined. _________________ Defund the FCC. |
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Clad in Sky l33t


Joined: 04 May 2007 Posts: 851 Location: Germany
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Posted: Thu Oct 10, 2013 11:56 am Post subject: |
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I wonder if it does anything on Intel CPUs that are not Pentium4.
I've got a i5-3210M CPU here, so it's not a Pentium 4 - it's a dual core but manages 4 threads at once. So is this the kind of hyperthreading SMT support enables? _________________ Kali Ma
Now it's autumn of the aeons
Dance with your sword
Now it's time for the harvest |
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Ant P. Watchman

Joined: 18 Apr 2009 Posts: 5451
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Posted: Thu Oct 10, 2013 2:21 pm Post subject: |
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Intel and SPARC are SMT/hyperthreading, i.e. 1 real core has a few extra registers added to make thread switching cheaper. The kernel SMT option is designed with those chips in mind. The AMD chips are built the other way around; it makes sense to treat them as non-SMT cores, because technically it's the same thing as having two real 386 cores that share a 387 co-processor. |
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pilla Administrator


Joined: 07 Aug 2002 Posts: 7659 Location: Pelotas, BR
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Posted: Wed Oct 30, 2013 2:36 pm Post subject: |
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Moved from Documentation, Tips & Tricks to Kernel & Hardware. _________________ "I'm just very selective about the reality I choose to accept." -- Calvin |
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