Re: Fixing excessive shootdowns during FFS read (kern/53124) on x86 - emap, direct map

[Martin Husemann <martin%duskware.de@localhost>]

On Mon, Apr 02, 2018 at 09:28:43PM +0200, Jaromír Dole?ek wrote:
> The only port actually having optimization for emap is x86. Since amd64
> is also the only one supporting direct map, we are really at liberty to pick
> either one.

I am not sure what you mean here - AFIK alpha and mips64 also have a direct
map for all available ram set up (and some arm too, plus I guess the new
aarch64 code as well).

I have not seen arguments why to do it on sparc64 yet, as we can easily
access all memory w/o any mapping, and a direct map has security implications.

> I'd lean towards direct map, since that doesn't require
> adding/removing any mapping in pmap_kernel() at all. From looking on the code,
> I gather direct map is quite easy to implement for other archs like
> sparc64. I'd say
> significantly easier than adding the necessary emap hooks into MD pmaps.

What would that hooks be? Are they documented?

Martin