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Re: [PATCH 1/6] x86/Kconfig: add selection of default x2APIC destination mode
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 29 Jun 2022 10:47:01 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 29 Jun 2022 08:47:22 +0000
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On Thu, Jun 23, 2022 at 04:47:22PM +0200, Jan Beulich wrote:
> On 23.06.2022 10:24, Roger Pau Monne wrote:
> > Allow selecting the default x2APIC destination mode from Kconfig.
> > Note the default destination mode is still Logical (Cluster) mode.
> >
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> > xen/arch/x86/Kconfig | 29 +++++++++++++++++++++++++++++
> > xen/arch/x86/genapic/x2apic.c | 6 ++++--
> > 2 files changed, 33 insertions(+), 2 deletions(-)
> >
> > diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
> > index 1e31edc99f..f560dc13f4 100644
> > --- a/xen/arch/x86/Kconfig
> > +++ b/xen/arch/x86/Kconfig
> > @@ -226,6 +226,35 @@ config XEN_ALIGN_2M
> >
> > endchoice
> >
> > +choice
> > + prompt "x2APIC default destination mode"
>
> What's the point of using "choice" here, and not a single "bool"?
I think choice better reflects the purpose of the option, it's
selecting between two different modes. It could be expressed with a
bool, but I think it's less clear.
> > + default X2APIC_LOGICAL
> > + ---help---
>
> Nit: Please don't use ---help--- anymore - we're trying to phase out its
> use as Linux has dropped it altogether (and hence once we update our
> Kconfig, we'd like to change as few places as possible), leaving just
> "help".
>
> One downside of "choice" (iirc) is that the individual sub-options' help
> text is inaccessible from at least the command line version of kconfig.
Hm, I usually use menuconfig when wanting to poke at options help.
I guess I could introduce a single X2APIC_PHYSICAL bool that starts
with default false and notes that otherwise the destination mode is
logical.
> > + Specify default destination mode for x2APIC.
> > +
> > + If unsure, choose "Logical".
> > +
> > +config X2APIC_LOGICAL
> > + bool "Logical mode"
> > + ---help---
> > + Use Logical Destination mode.
> > +
> > + When using this mode APICs are addressed using the Logical
> > + Destination mode, which allows for optimized IPI sending,
> > + but also reduces the amount of vectors available for external
> > + interrupts when compared to physical mode.
> > +
> > +config X2APIC_PHYS
>
> X2APIC_PHYSICAL (to be in line with X2APIC_LOGICAL)?
Right, was about to expand it but did consider PHYS to be clear enough
(opposed to using LOG or LOGIC), will expand in next version.
Thanks, Roger.
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