* Andrew Morton ([email protected]) wrote:
> On Fri, 1 Jun 2007 02:14:53 +0200 (MEST)
> Mikael Pettersson <[email protected]> wrote:
>
> > Andrew Morton wrote:
> > > Mathieu Desnoyers <[email protected]> wrote:
> > >
> > > > * Andrew Morton ([email protected]) wrote:
> > > >
> > > > > > Use the faster conditional calls for F00F bug handling in do_page_fault.
> > > > > >
> > > > >
> > > > > I guess this means that CONDCALL will be enabled on pretty much all i386,
> > > > > in which case making the whole feature Kconfigurable is starting to look
> > > > > marginal.
> > > > >
> > > > > Perhaps a better approach would have to made this change dependent upon
> > > > > CONDCALL, rather than forcing it on.
> > > > >
> > > >
> > > > Do you mean making X86_F00F_BUG depend on COND_CALL instead of selecting
> > > > it ?
> > >
> > > yup
> >
> > X86_F00F_BUG needs to be enabled in all kernels capable of booting on
> > P5 class machines, whether or not some obscure CONFIG_COND_CALL thingy
> > is enabled or not. X86_F00F_BUG is not some optional optimisation, it's
> > an essential workaround for a serious hardware bug.
> >
> > Therefore it seems select rather than depend is called for.
>
> Nope.
>
> CONFIG_COND_CALL=n -> do f00f handling the present way
> CONFIG_COND_CALL=y -> do f00f handling the new, fast-n-fancy way
>
>
> Because I don't think everyone will want to drag all this cond_call stuff
> into their kernel just for slightly faster f00f handling.
>
Then I should probably leave the redundant
if (boot_cpu_data.f00f_bug)
test in do_f00f_workaround so that configuration where cond_calls are
not enabled still behave the same way as before. The redundant test will
make the case when cond calls are present a little slower, but we still
have the improvement when the architecture does not need the workaround.
I could also wrap this test in a #ifndef CONFIG_COND_CALL, but it seems
ugly.
Also, since the default is not to set the CF_STATIC_ENABLE flag, the
workaround won't be compiled in the kernel if the conditional calls are
configured out.
The question that arises is : what should be the default behavior of a
cond_call when the cond_calls are configured out? Active, active only
if the CF_STATIC_ENABLE flags is set or inactive?
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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