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    SubjectRe: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata
    On Tue, 16 Sep 2003, Dave Jones wrote:

    > On Tue, Sep 16, 2003 at 12:46:36PM +0100, Jamie Lokier wrote:
    >
    > > > The user space problem worries me more, because the expectation
    > > > is that if CPUID says the program can use perfetch, it could
    > > > and should regardless of what the kernel decided to do here.
    > >
    > > If the workaround isn't compiled in, "prefetch" should be removed from
    > > /proc/cpuinfo on the buggy chips.
    >
    > prefetch isn't a cpuid feature flag. The only way you could do
    > what you suggest is by removing '3dnow' or 'sse', which cripples
    > things more than necessary.

    Good point, and even if it were a separate feature, any code which was
    clever enough to use prefetch is likely to check the CPU bits rather
    than the /proc anyway. That's a guess, I suspect most programs do
    whatever gcc/glibc choose.

    If the fixup were not in place, would it be useful to emit a warning
    like "you have booted a non-Athlon kernel on an Athlon process, user
    programs may get unexpected page faults." That's in init code, hopefully
    there is no critical size issue there, I assume, other than how large a
    kernel can be booted by the boot loader.

    --
    bill davidsen <davidsen@tmr.com>
    CTO, TMR Associates, Inc
    Doing interesting things with little computers since 1979.

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