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    SubjectRe: Intel P6 vs P7 system call performance

    On Tue, 17 Dec 2002, Dave Jones wrote:
    > I'm sure I recall seeing errata on at least 1 CPU re sysenter.
    > If we do decide to go this route, we'll need to blacklist ones
    > with any really icky problems.

    The errata is something like "all P6's report SEP, but it doesn't
    actually _work_ on anything before the third stepping".

    However, that should _not_ be handled by magic sysenter-specific code.
    That's what the per-vendor cpu feature fixups are there for, so that these
    kinds of bugs get fixed in _one_ place (initialization) and not in all the
    users of the feature flags.

    In fact, we already have that code in the proper place, namely

    /* SEP CPUID bug: Pentium Pro reports SEP but doesn't have it */
    if ( c->x86 == 6 && c->x86_model < 3 && c->x86_mask < 3 )
    clear_bit(X86_FEATURE_SEP, c->x86_capability);

    so the stuff I sent out should work on everything.

    (Modulo the missing syscall page I already mentioned and potential bugs
    in the code itself, of course ;)


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