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Re: [PATCH] vPCI: make vpci_add_register() an out-of-line function
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
- Date: Thu, 18 Dec 2025 11:02:40 -0500
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 18 Dec 2025 16:03:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12/18/25 05:45, Jan Beulich wrote:
> Calling a function with 10 arguments is inefficient on many architectures:
> x86-64 allows for up to 6 register parameters, Arm64 for up to 8.
> Everything else needs passing on the stack, i.e. forcing the compiler to
> emit stack manipulation insns at every call site.
>
> Shrinks generated code on x86 (with gcc15) by over 250 bytes. The gains on
> Arm64 are a little less.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
> ---
> Why is it, btw, that the declarations live in xen/vpci.h? These functions
> aren't supposed to be called from outside xen/drivers/vpci/, are they? In
> which case their decls may better live in a private header?
You have a good point, they could very well live in a private header IMO.
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