Re: [RFC]: Removing old Falkor ifuncs

[Wilco Dijkstra <Wilco.Dijkstra@arm.com>]

Hi Siddhesh,

>On 2022-12-09 10:14, Wilco Dijkstra wrote:
>> Do we need the ifuncs for Falkor? The SIMD memcpy is now the default
>> generic memcpy and that is quite similar to the Falkor one, so it seems
>> time to remove the Falkor variants. Since you are the original author,
>> what do you think?
>
> The key differentiator in memcpy/memmove at that time was the register 
> number usage since that affected how the hardware prefetcher performed. 
> Changing that might affect performance on falkor, although I don't 
> exactly remember by how much.

If there was a difference, it would likely be on large copies. But it would be hard
to test without access to a machine...

> The other key differentiator is in memset, where reading dczid_el0 was 
> expensive on falkor, so the value is hard coded to avoid reading it 
> everytime.

Yes this is true for various microarchitectures. I posted a patch to make this
more general a few years ago, ie. always use an ifunc if the ZVA size is 64
rather than do something CPU specific.

Cheers,
Wilco