Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata

Bill Davidsen
2003-09-16T14:02:17Z

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.