[Discuss] Next AMD FX-8120 update

[gaf at blu.org (Jerry Feldman)]

On 03/18/2012 12:02 PM, Richard Pieri wrote:
> What you will typically find is that if your threads are CPU bound then you will see better performance over the long term with HT disabled.  The reason is that the phantom CPUs that HT provides need to share cache and memory bandwidth and there is some extra switching overhead.  The upshot is that if you have 1 CPU with 2 HT threads and 4 CPU-bound jobs to run, the total time to run all 4 jobs will be less with HT disabled.  As an aside for anyone running a Condor pool, disabling HT is recommended for this reason.
>
> On the other hand, if you are not CPU-bound across all of your threads, or in environments where concurrency is more important than throughput, then HT may be a win.
>
> AMD's Bulldozer architecture has less resource contention than Intel's HT implementations (less overhead) but two threads on 1 core still have to share some resources and you will usually see results similar to what I described.
In Toronto they always turn off HT. I ran a quick test and found that
the RiskWatch application runs better with no HT. There is certainly
some benefit to HT under some circumstances.

-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
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