Re: AVX support

[Alexander Nasonov <alnsn%yandex.ru@localhost>]

David Laight wrote:
> 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.)

I'm sure it's quite complicated. 

> 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.

Is it the case for all arches or only if there is no pcu(9) support? In
the latter case, would switching to pcu(9) interface help to combat this
problem?

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

Are you talking about userspace cores and gdb code? This sounds
like a work for a phase II.

At this point, I'm just playing with AVX instruction and I can
happily use (and test) any half-baked patch if you have one.

Alex