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

## vexatious

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

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

> SMT (Hyperthreading) scheduler support
> 
>   │ CONFIG_SCHED_SMT:
> 
>   │
> ...

  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

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.

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

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

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