Re: Kernel Benchmarks With P4+SMP+SMT?

[Bill Davidsen]

Justin Piszcz wrote:
> Has anyone performed any benchmarks with:
>
> No SMP w/HT?
> SMP w/HT?
> SMP + SMT w/HT?
>
> [ ] Symmetric multi-processing support
> [ ]   SMT (Hyperthreading) scheduler support
>
>   x SMT scheduler support improves the CPU scheduler's decision making
>   x when dealing with Intel Pentium 4 chips with HyperThreading at a
>   x cost of slightly increased overhead in some places. If unsure say
>   x N here.
>
> I'm tempted to try SMT and benchmark these sometime but I am asking the 
> list if anyone has already done this first.
>
> Question: "slightly increased overhead in some places."
>
> What type of workloads would exhibit such overhead?
>
> Would this option (SMT) be recommended for a desktop or server machine?
>
> Are there any white papers or documentation I can read about this option?

I run SMT on all my HT uni systems. Depending on what you do it can help 
up to 30% (kernel build) or just enough to measure. This is one of those 
"it depends" things, I bet there are loads which run better without, and 
there is a tad of overhead in the SMP kernel locking.

If you run SMP, you have that overhead anyway, so I doubt it hurts.

YMMV

--
bill davidsen <davidsen@xxxxxxx>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979
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