Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5

Ingo Molnar
2004-08-31T20:14:52Z

* Ingo Molnar <mingo@elte.hu> wrote:

> it's more complex than that - MTRR's are caching attributes that the
> CPU listens to. Mis-setting them can cause anything from memory
> corruption to hard lockups. The question is, does any of the Intel (or
> AMD) docs say that the CPU cache has to be write-back flushed when
> setting MTRRs, or were those calls only done out of paranoia?

the Intel docs suggest a cache-flush when changing MTRR's, so i guess
we've got to live with this. _Perhaps_ we could move the cache-disabling
and the wbinvd() out of the spinlocked section, but this would make it
preemptable, possibly causing other tasks to run with the CPU cache
disabled! I'd say that is worse than a single 0.5 msec latency during
MTRR setting.

Ingo