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    SubjectRe: hyperthreading
    Måns Rullgård writes:
    > Gábor Lénárt <> writes:
    > >> > flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
    > >> > cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
    > >> > bogomips : 3334.14
    > >>
    > >>
    > >> P4 does not support HT ... only Xeon and new generation P4-HT does.
    > >
    > > OK, but if this CPU does not support HT, then why 'ht' is shown at
    > > flags in /proc/cpuinfo? It looks like quite illogical for me then ...
    > I've been wondering about that myself. I'm sure my P4M doesn't have
    > any hyperthreading.

    Don't people read Intel docs any more?

    - The HT feature flag means "might have HT, check further to make sure".
    - "check further" involves checking #siblings >= 2 via CPUID.
    Old P4s typically announce HT but have #siblings < 2.
    - Intel made HT enabling a hardware thing via the chipset (a pin
    sampled at reset). BIOS can disable HT but only HW can enable it.
    This is why you can't put a HT-capable P4 in a non-HT-chipset
    machine and expect it to work -- although PowerLeap seemed to
    have an adapter to "fix" that.
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