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Re: [PATCH for-4.19] xen/arch: Centralise __read_mostly and __ro_after_init
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 14 Jun 2024 15:39:03 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 14 Jun 2024 13:39:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14.06.2024 14:49, Andrew Cooper wrote:
> These being in cache.h is inherited from Linux, but is an inappropriate
> location to live.
>
> __read_mostly is an optimisation related to data placement in order to avoid
> having shared data in cachelines that are likely to be written to, but it
> really is just a section of the linked image separating data by usage
> patterns; it has nothing to do with cache sizes or flushing logic.
>
> Worse, __ro_after_init was only in xen/cache.h because __read_mostly was in
> arch/cache.h, and has literally nothing whatsoever to do with caches.
>
> Move the definitions into xen/sections.h, which in paritcular means that
> RISC-V doesn't need to repeat the problematic pattern. Take the opportunity
> to provide a short descriptions of what these are used for.
>
> For now, leave TODO comments next to the other identical definitions. It
> turns out that unpicking cache.h is more complicated than it appears because a
> number of files use it for transitive dependencies.
I don't particularly mind this approach, so ...
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Yet this (or variants thereof) is precisely what I wouldn't have wanted to do
myself, for leaving garbled state and, if I'm not mistaken, introducing new
Misra violations because of the redundant #define-s.
Jan
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