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

[davidsen@tmr.com (bill davidsen)]

In article <3F6087FC.7090508@pobox.com>,
Jeff Garzik  <jgarzik@pobox.com> wrote:
| Andi Kleen wrote:
| > It was not created for that (I know that because I created it ;-)
| 
| hehe
| 
| 
| > X86_GENERIC is merely an optimization hint (currently it only changes the cache
| > line size hint) It does not change anything related to correctness. Everything
| > that handles correctness is checked unconditionally.
| 
| When, building non-Pentium4-related code when CONFIG_MPENTIUM4 && 
| !CONFIG_X86_GENERIC, it's OK that the code is incorrect for (picking 
| example) AMD processors.
| 
| It would be a user bug to boot that on an AMD box, just like it would be 
| user bug to boot a CONFIG_M586 kernel on an ancient 386.
| 
| 
| > is_prefetch is a correctness thing.
| 
| When we know at compile time it's not needed, it should not be enabled.

Clearly that's right. This buys nothing on CPUs which don't have the
problem, why have *any* overhead in size and speed? It's too bad that
people have to read around all that code, they don't need to give it a
home in their RAM and execute it as well.
-- 
bill davidsen <davidsen@tmr.com>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.