Messages in this thread | | | Date | Mon, 11 Sep 2006 09:29:59 +0200 | From | Ingo Molnar <> | Subject | Re: 2.6.18-rc6-mm1: GPF loop on early boot |
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* Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> Ingo Molnar wrote: > >another thing about i386-pda: why did you pick the %gs selector to store > >the PDA in? %fs would be a better choice because %gs is used by glibc so > >the saving/restoring of %fs would likely be near zero-cycles cost. > >(instead of the current 9 cycles for saving/restoring %gs) > > Why would saving/restoring %fs be quicker? [...]
because userspace does not use it normally, while with %gs we'd switch between glibc's descriptor [which must be shadowed by the CPU] and the kernel's descriptor [which must be shadowed by the CPU too] - hence causing a constant reloading of the shadow register.
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