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Re: [PATCH] vPCI: make vpci_add_register() an out-of-line function
- To: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Tue, 23 Dec 2025 16:28:59 +0100
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 23 Dec 2025 15:29:16 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Dec 18, 2025 at 11:02:40AM -0500, Stewart Hildebrand wrote:
> 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>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> > 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.
In fact most of vpci.h could become private.
vpci_{,de}assign_device() must obviously be public, plus a couple more
to satisfy calls from external sites: vpci_{read,write}(),
vpci_dump_msi(), vpci_process_pending() and vpci_reset_device().
Maybe something else I'm missing, but not a lot more.
Thanks, Roger.
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