Piledriver faster with no SMT-HT scheduler; only MT?

vexatious · Tux's lil' helper Joined: 24 Aug 2010 Posts: 77

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
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DONAHUE · Posted: Wed Jun 19, 2013 10:55 pm Post subject:

Help for what I assume is the configuration choice you are discussing says:

Clad in Sky · l33t Joined: 04 May 2007 Posts: 843 Location: Germany

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?
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Ant P. · Watchman Joined: 18 Apr 2009 Posts: 5231

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.

pilla · Posted: Wed Oct 30, 2013 2:36 pm Post subject:

Moved from Documentation, Tips & Tricks to Kernel & Hardware.
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