MIPS future...

[Brooks Davis]

On Wed, Dec 12, 2018 at 11:15:06AM -0700, Warner Losh wrote:
> OK. To be a good player in the FreeBSD ecosystem, we need to do  a few
> things.
> 
> First, we need to implement atomic_swap_64. hps did this for mips64 and
> committed it. He sent me some further patches for it that I need to commit
> when I get a change, maybe at the airport tonight.
> 
> But this brings up a couple of issues I'd like to bring up.
> 
> First, to implement atomic_swap_64 on mips-32 is hard. In that it's not
> just the canonical ldd/sdd sequence because those aren't available there.
> We can do the standard trick of reading STATUS0, clearing IE, storing it,
> do the operation and then restoring STATUS0. This is efficient enough for
> the use in the kernel for the supported cores we have.

I think we have to do this no matter how expensive it is or kill 32-bit
mips.  There is no way there are enough 32-bit mips users to justify
even the minor level of developer friction the unr64 caused.

> That brings me to my next question: SWARM. Can we kill SWARM entirely? It's
> for the BCM1250 part, released in sometime before 2000. It was super
> popular because it was the reference for a ton of things that followed. I
> think it's run is over and we can remove it. I can find no users of it in
> the nyc dmesg database. Mine has been in a plastic bag since before my sone
> was born in 2006... So I'm thinking we can remove this platform. It was on
> the edge last time I did a GC in mips-land.

It looks like it's a sibyte platform if I read the config files
correctly.  If so, I seriously doubt it works reliably under meaningful,
multi-process load.  We built at sibyte-like PIC for BERI and there were
quite a few WTF moments as we adapted to code.

I don't have strong opinions on the other platforms.  I know we haven't
used GXEMUL in at least 5 years on our projects.  Qemu and the MALTA
config does everything we need.

-- Brooks
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