[RFC PATCH v2 05/10] lib: vdso: inline do_hres()

[Andy Lutomirski]

On Mon, Dec 23, 2019 at 6:31 AM Christophe Leroy
<christophe.leroy at c-s.fr> wrote:
>
> do_hres() is called from several places, so GCC doesn't inline
> it at first.
>
> do_hres() takes a struct __kernel_timespec * parameter for
> passing the result. In the 32 bits case, this parameter corresponds
> to a local var in the caller. In order to provide a pointer
> to this structure, the caller has to put it in its stack and
> do_hres() has to write the result in the stack. This is suboptimal,
> especially on RISC processor like powerpc.
>
> By making GCC inline the function, the struct __kernel_timespec
> remains a local var using registers, avoiding the need to write and
> read stack.
>
> The improvement is significant on powerpc.

I'm okay with it, mainly because I don't expect many workloads to have
more than one copy of the code hot at the same time.