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

[Andi Kleen]

Ingo Molnar <mingo@xxxxxxx> writes:

> * Ingo Molnar <mingo@xxxxxxx> wrote:
>
>> 
>> * Lee Revell <rlrevell@xxxxxxxxxxx> wrote:
>> 
>> > File under boot-time stuff, I guess.  This could be bad if X crashes,
>> > but I can't remember the last time this happened to me, and I use xorg
>> > CVS.
>> 
>> but the first wbinvd() within prepare_set() seems completely unnecessary
>> - we can flush the cache after disabling the cache just fine.
>
> the third wbinvd() in post_set() seems unnecessary too - what kind of
> cache do we expect to flush, we've disabled caching in the CPU ... But
> the Intel pseudocode does it too - this is a thinko i think.

The multiple steps are needed, otherwise there can be problems
with hyperthreading (the first x86-64 didn't do it in all cases,
and it causes occassional problens with Intel CPUs) 

Also repeated calls of this are relatively cheap because at the
second time there is not much to flush anymore.

I would suggest to not do this change, it could cause very
subtle problems.

-Andi

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