[yocto] [meta-raspberrypi] Why not enable hard floating point?

[Andrei Gherzan]

On Sun, Jan 18, 2015 at 2:29 AM, Andrei Gherzan <andrei at gherzan.ro> wrote:

> Hello,
>
> On Fri, Jan 16, 2015 at 3:05 AM, J. Tang <tang at jtang.org> wrote:
>
>>
>> On 2015-01-15, at 04:06, Mike Looijmans <mike.looijmans at topic.nl> wrote:
>>
>> > -2- The CPU doesn't actually have floating point support and the kernel
>> is emulating it for you. This allows the platform to run "hf" binaries, at
>> a minor performance cost compared to completely doing the emulation in user
>> space (libc).
>>
>> From my understanding, the Raspberry Pi (at least the model B, which is
>> what I have) has an FPU.
>>
>> Would it hurt to at least mention in the top-level README of the
>> meta-raspberrypi layer that a user could enable hard FP by setting the
>> DEFAULTTUNE?
>>
>>
> Definitely it wouldn't. But right now we have two options:
> We can just throw a README line and that's it.
> Or we can  investigate a little to see if in our current setup we actually
> use FPU instructions or not. Following Mike's answer I would definitely
> think that we are in case 1 where the compile based on the CPU
> configuration figures out that we can use FPU instruction on this CPU
> architecture. Right now, as being on vacation, I can really test on
> binaries by dissembling code and check it by hand. Anybody who can do it
> and provide some feedback? As well, some bench-marking would really make
> sense here.
>

It was confirmed on another thread (
https://lists.yoctoproject.org/pipermail/yocto/2015-January/023201.html)
that there is no performance improvements while switching to HFP. This
basically proves what Mike Looijmans described in (1). So, we are on the
safe side with our current setup.


-- 
*Andrei Gherzan*
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