Re: Building kernels with FPU support?

On 23 Oct 2024, at 19:05, Vadim Goncharov wrote:

> On Wed, 23 Oct 2024 10:38:12 -0400
> gnn <gnn@freebsd.org> wrote:
>
>> Howdy,
>>
>> I am wondering if anyone has tried, lately, to see what effect
>> building with FPU support has on overall system performance.  I've
>> been working with a kernel module that needs this (for reasons I'll
>> not go into now) and it occurred to me that the perceived performance
>> overhead that caused us to only do fixed point in the kernel may no
>> longer be significant.  I note that Linux has an option to build
>> their kernel with FPU support.
>>
>> And yes, I know that we have the ability to selectively deal with the
>> FPU, from the calls outlined in Section 9 for fpu, but I'm asking the
>> more general question of "does it matter?" and "if so, how much?"
>
> Would be great to have it for e.g. having portions of SQLite in kernel,
> e.g. it's R*Tree module for fast 5-dimensions lookup (like for firewall
> rules) uses floats.

Funny you should mention sqlite in the kernel, since that's the exact use case that started me down this path, and is covered in a paper I've co-authored that's been accepted for publication at a database conference in 2025.

I am sure there are other use cases, we already have this on for the openssl module, for example.

Best,
George