linuxaudio.org

On 06/29/2011 10:33 PM, Nick Copeland wrote:

quoted text
>> No, when building with Android NDK using the armeabi-v7a ABI, hard

> floats are

>> used. This works on ARMv7, which means a lot of devices, and certainly the

>> majority.

>

> But then every other system gets the rough 1000 factor performance hit

> that started

> this thread since all other CPU have to do a system call to execute the

> float operation.

> Designing for a single handset family is not that scalable.

I don't know what syscall you are talking about.
When you build with the android NDK, you can choose to compile for armeabi, for

armeabi-v7a or for both. If you only build for the later, then your app is not

visible to non ARMv7 devices on the market. I can't remember what happens if you

try to install the APK manually on an ARMv5 device, but I think this fails or

doesn't run.
If the app's built for both ABIs, then the package installer installs the proper

set of libraries provided by your app, either armeabi or armeabi-v7a depending

on the hardware.
Also, there's a small library provided by the NDK, called cpu-features, which

allows you to detect CPU features at run time. I used that and rely on it to

activate certain features. It works great.
>> > The ARM

quoted text
>> > softfloat overhead is not that great and the coding required to get

>> > access to the GPUs is suitable that developers will implement them

>> > for optimisations.

>>

>> Soft floats are insanely slow on Android in my experience.

>

> A factor of 10 or 20 over hard floats? Sound about right? The factor

> 1000 is for code

> that uses FPU instructions on systems without the FPU support. That I

> would call

> insanely slow but you can choose which way you go here.

AFAIK, on Android, there's no such thing as executing FPU instructions on

devices without an FPU, unless you are doing something very weird.
This 1000 factor and the syscalls you mention is something I never heard about,

which is maybe true in general about ARM, but which doesn't happen in practice

on Android, if you use the standard build tools and OS.
That said, a factor of 10 or 20 is enough for me to call it insane, yes :p
>> You got an FPU on most devices, you can compile for hard floats,

quoted text
> activate ARM

>> NEON if you wish too, and even check for cpu features at runtime. I

> don't see

>> why you want to use the GPU for optimization.

>

> Man, the recent chipsets have 6 of these pipelines - designed for

> graphics processing

> but sitting there waiting for audio DSP.

Okay, right, that's interesting. But, well, you got plenty of FPUs out there,

and you just need a single line in a makefile to use them. That was my point.
--

  Olivier

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