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    SubjectRe: Microsecond accuracy
    On 7 Dec 2000, H. Peter Anvin wrote:

    > Unfortunately the most important instance of the in-kernel flag -- the
    > global one in the somewhat misnamed boot_cpu_data.x86_features --
    > isn't actually readable in the /proc/cpuinfo file. It is perfectly
    > possible (e.g. the "notsc" option) for ALL the CPUs to report this
    > capability, but the global capability to still be off.

    Hmm, I recall I implemented and explicitly verified switching the
    /proc/cpuinfo "tsc" flag (as well as the userland access to the TSC) off
    when I wrote the code to handle the "notsc" option. Has it changed since
    then? I recall you modified the code a bit -- I looked at the changes
    then but I was pretty confident the semantics was preserved.

    There is no possibility to have TSC and non-TSC chips mixed in a single
    SMP system (due to existing hardware, even though it's possible in
    theory), so there is no problem with such an assymetry. Either all chips
    have the "tsc" flag in /proc/cpuinfo on or off.

    + Maciej W. Rozycki, Technical University of Gdansk, Poland +
    + e-mail:, PGP key available +

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