[Cbe-oss-dev] [RFC, PATCH 1/2] powerpc/spufs: allow spu_acquire_saved to correctly handle NOSCHED contexts

[Arnd Bergmann]

On Friday 01 August 2008, Jeremy Kerr wrote:
> Currently, we don't want to call spu_acquire_saved on NOSCHED contexts,
> as these contexts can't be spu_deactivated arbitrarily.
> 
> This change adds support for NOSCHED contexts in spu_acquire_saved - we
> can call this on NOSCHED contexts, as long as the context is already
> saved, or not being run.

I think this is an incompatible change that we should not consider. We have
users relying on the phys-id of the context not to change and that can not
accept the latencies of a context save/restore when accessing the context.

Also, the QPACE project requires the current semantics in order to do
accesses to SPUs through DMA from external devices.

Regarding the interaction with ISOLATED contexts, you now change how
the flag is interpreted. Right now, ISOLATED contexts rely on NOSCHED
behavior and we had split those into two flags so that you can get
real NOSCHED behaviour without using ISOLATED, but you give that up
now.

What kind of benefit do you see from your patch, other than saving a few
lines of source code with the second patch?

	Arnd <><