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    SubjectRe: [PATCH 4/7] perf: Check if HT is supported and enabled
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    On Tue, 2010-12-28 at 16:51 +0800, Lin Ming wrote:
    > > +static bool ht_enabled(int cpu)
    > > +{
    > > + int total_logical_processors, total_cores;
    > > + unsigned int eax, ebx, ecx, edx;
    > > +
    > > + cpuid(1, &eax, &ebx, &ecx, &edx);
    > > +
    > > + /* Bit 28 in EDX indicates if it's HT capable */
    > > + if (!(edx & 0x10000000))
    > > + return false;
    > > +
    > > + total_logical_processors = (ebx >> 16) & 0xff;
    > > +
    > > + ecx = 0;
    > > + cpuid(4, &eax, &ebx, &ecx, &edx);
    > > + total_cores = ((eax >> 26) & 0x3f) + 1;
    > > +
    > > + /* Thread nums per core */
    > > + return (total_logical_processors / total_cores) > 1;
    > > +}
    > > +
    >
    > This function can be simplified as below,
    >
    > static bool ht_enabled()
    > {
    > if (!cpu_has(&boot_cpu_data, X86_FEATURE_HT))
    > return false;
    >
    > return smp_num_siblings > 1;
    > }
    >
    > But this still can't detect if HT is on or off.
    > smp_num_siblings is always 2 even if HT is disabled in BIOS.
    >
    > Any idea how to detect if HT is on or not?

    Not quite sure, the intel docs aren't really clear on how the HW
    supports HT, has 2 siblings but BIOS disabled it thing works. I just
    tried reading the arch/x86 code but that only got me more confused.

    hpa, could you comment?


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