Re: [POWERPC] convert string i/o operations to C

Segher Boessenkool wrote:

quoted

For a generic "powerpc" kernel it can be understood, but when you
consider that on 970/POWER4 and above they use lwsync instead of sync

lwsync (sync 1) doesn't (architecturally) do anything to order MMIO
accesses, so you're misunderstanding something.

See below :D

quoted

(google for them and see the mailing list posts :), just to breathe back
some performance in spinlocks and so on, surely this can be rejigged so
that processors don't do more work than necessary..? Even a noop takes
time doesn't it?

No-ops don't matter for performance, compared to the cost of the I/O
itself.  It would help to avoid heavier-than-necessary synchronisation
instructions if not needed on some certain CPU (or on non-SMP kernels,
etc.)

But it couldn't hurt, right? There has to be an application note per-CPU 
on the correct sequence of operations for such an access (I seem to have 
collected a directory full for firmware development), it seems a little 
odd to pick and choose one instruction over another for one thing, and 
then say you need to do it to support the 601 of all things, and run 
this code against the G3/G4/G5 which perhaps doesn't care or is more 
intelligent about it (or is guaranteed to have a more intelligent host 
bridge at least).

Maybe I'm talking crap, please say so :D

-- 
Matt Sealey [off-list ref]
Genesi, Manager, Developer Relations