Re: [PATCH 3/5] xen/sort: Switch to an extern inline implementation

[Julien Grall <julien@xxxxxxx>]

Hi Andrew,

On 11/11/2021 17:57, Andrew Cooper wrote:
> There are exactly 3 callers of sort() in the hypervisor.
>
> Both arm callers pass in NULL for the swap function.  While this might seem
> like an attractive option at first, it causes generic_swap() to be used which
> forced a byte-wise copy.  Provide real swap functions which the compiler can
> optimise sensibly.
>
> Furthermore, use of function pointers in tight loops like that can be very bad
> for performance.  Implement sort() as extern inline, so the optimiser can
> judge whether to inline things or not.
>
> On x86, the diffstat shows how much of a better job the compiler can do when
> it is able to see the cmp/swap implementations.
For completness, here the Arm bloat-o-meter:

add/remove: 0/5 grow/shrink: 2/0 up/down: 928/-660 (268)
Function                                     old     new   delta
boot_fdt_info                                640    1132    +492
register_mmio_handler                        292     728    +436
u32_swap                                      20       -     -20
generic_swap                                  40       -     -40
cmp_mmio_handler                              44       -     -44
cmp_memory_node                               44       -     -44
sort                                         512       -    -512
Total: Before=966915, After=967183, chg +0.03%

Cheers,

--
Julien Grall