On Thu, 31 Jan 2002, Jason Evans wrote:

> On Wed, Jan 30, 2002 at 11:14:48PM +0100, Gérard Roudier wrote:
> >
> > Linux can be fixed, but the useless writes of the existing Athlons from
> > the very fast cache to the relatively very slow memory cannot. And all
> > Athlon users may well pay this penalty under any OS...  unless we want to
> > disable caching. :)
> Have you done benchmarks to show that the speculative writes are useless
> often enough to cause enough memory bus contention that overall performance
> is degraded, despite the speedups when the speculative writes are valid?

I haven't done any benchmark of this sort, neither intend to do any since
I haven't time for that. But I wrote in my email that my 2 Athlon systems
worked fine and fast, just to indicate that for normal use I didn't see
any performance problem at all.

> I
> suspect that AMD in fact performed such tests; otherwise they wouldn't have
> gone to the trouble of implementing speculative writes.

The Athlon rewriting same value to cacheable memory under the knees of
programmers looks a severe issue to me if it is true. Not only AGP memory
can be affected. What about SMP, MMIO (if some cacheable mapping exists),

In my opinion, OSes having some cacheable mapping to AGP memory is not the
real problem. Just it has revealed the AMD issue.


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