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    SubjectRe: How to detect multi-core and/or HT-enabled CPUs in 2.4.x and 2.6.x kernels
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    >
    > one piece of information that Ganglia collects for a node is the
    > "number of CPUs", originally meaning "physical CPUs".

    Ok I was afraid of that.

    > With the
    > introduction of HT and multi-core things are a bit more complex now. We
    > have decided that HT sibblings do not qualify as "real" CPUs, while
    > multi-cores do.

    I think that decision is a mistake, and is probably based on experiences
    with the first generation of HT capable Pentium 4 processors.

    The original p4 HT to a large degree suffered from a too small cache
    that now was shared. SMT in general isn't per se all that different in
    performance than dual core, at least not on a fundamental level, it's
    all a matter of how many resources each thread has on average. With dual
    core sharing the cache for example, that already is part HT. Putting the
    "boundary" at HT-but-not-dual-core is going to be highly artificial and
    while it may work for the current hardware, in general it's not a good
    way of separating things (just look at the PowerPC processors, those are
    highly SMT as well), and I suspect that your distinction is just going
    to break all the time over the next 10 years ;) Or even today on the
    current "large cache" P4 processors with HT it already breaks. (just
    those tend to be the expensive models so more rare)

    I would strongly urge you to reconsider this decision; if you want to
    show "sockets" that sounds reasonable, or even if you want to do it on
    the "bus sharing" level (FSB/HT), but HT.. just sounds wrong.





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