Re: AVX support

[David Laight <david%l8s.co.uk@localhost>]

On Wed, Jan 01, 2014 at 11:18:16AM +0000, Alexander Nasonov wrote:
> Hi,
> 
> I recently bought a Haswell notebook and wanted to play with new
> AVX/AVX2 instructions but I quickly found out that they are disabled
> on NetBSD. I see some recent discussions about this but I don't see
> any commit messages or patches. I wonder if anyone working on this?

Slowly ...
Unfortunately it isn't as simple as one might expect.
Random differences between the amd64 and i386 code don't help matters.
(You are in a maze of structures that define the same physical data.)

Amongst other problems there are a few places where a full copy of the
FP (etc) state structure ends up on the stack (and IIRC in some code
paths several of them). Increasing the size from 512 bytes (quite large
for the kernel stack) to a potentially very large value - nearly 1024
just for AVX - might cause stack overflow problems.
Not helped by the actual FP save area being in the stack pages.

One of the really bad code paths is the core dump code.

        David

-- 
David Laight: david%l8s.co.uk@localhost