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Piledriver faster with no SMT-HT scheduler; only MT?
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vexatious
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PostPosted: Wed Jun 19, 2013 12:13 am    Post subject: Piledriver faster with no SMT-HT scheduler; only MT? Reply with quote

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
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PostPosted: Wed Jun 19, 2013 10:55 pm    Post subject: Reply with quote

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.
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Clad in Sky
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PostPosted: Thu Oct 10, 2013 11:56 am    Post subject: Reply with quote

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.
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PostPosted: Thu Oct 10, 2013 2:21 pm    Post subject: Reply with quote

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
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PostPosted: Wed Oct 30, 2013 2:36 pm    Post subject: Reply with quote

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