Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain supportto use NMI-safe methods

[Jeremy Fitzhardinge]

On 06/15/09 13:27, Linus Torvalds wrote:
> On Mon, 15 Jun 2009, Jeremy Fitzhardinge wrote:
>    
> > We have to restore the usermode %gs somewhere...
> >      
>
> None of this is useful for user-mode return _anyway_, since you have to
> restore %cs/%ss too. At that point, you have to use iret.
>    

Ah, right.  I'd even looked at that at one point, when I was 
investigating optimising kernel->kernel exit paths (I'd decided it 
wasn't worth it for its own sake, since they simply don't happen that 
often).

    J
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