Re: [git pull] scheduler updates

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> Doing it in get_cycles() and "forgetting about it" may sound like a 
> simple solution, but it's likely wrong. For example, one of the few 
> cases where we realy care about time going backwards is 
> gettimeofday() - which uses tsc, but which also has tons of 
> serializing instructions on its own. EXCEPT WHEN IT IS a vsyscall!
> 
> But in that case, we don't even have the barrier, because we put it 
> in the wrong function and 'forgot about it'. Of course, we may not 
> need it (rdtscp maybe always serializes, I didn't check), but the 
> point is, an explicit barrier is actually better than one that is 
> hidden.

no, we really had it in the vsyscall case: which uses vread, which 
uses __native_read_tsc(), which had the barriers.

And i think that's the _only_ valid place to have it.

So that's why my change moves it from the __native_read_tsc() over to 
_only_ the vget_cycles().

am i missing something on such a nice Saturday evening? :)

	Ingo
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