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

Jeremy Fitzhardinge
2009-06-15T21:07:08Z

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