I'll start implementation of this soonish.

has the dust settled about CACHESYNC_GLOBAL vs. implementing in 
the application using STOREBAR?

	Ignatios

On Thu, Dec 03, 1998 at 09:30:52PM +0100, Ignatios Souvatzis wrote:
> $Id: cacheflush.txt,v 1.3 1998/12/03 20:28:23 is Exp is $
> 
> RATIONALE (by eeh)
> 
> The primary stated purpose of this was to assist the implementation of
> things like JIT compilers.  That's quite reasonable.
> 
> ....
> 
> There are several higher-level operations that I could see an application
> might legitimately want to do.  
> 
> 	o It might want to synchronize the data and instruction caches
> 	  because it just finished generating some code that it will want
> 	  to execute.
> 
> 	o It might want to force a memory barrier to make sure any data it
> 	  has stored is now globally visible to other processors.
> 
> 	o It might want to force read synchronization while spinning on a
> 	  lock.
> 
> I think it would be better to think in terms of these operations rather
> than explicit operations on the caches.  Flushing a cache can have quite
> different results on different cache implementations, and some caches are
> simply not meant to be flushed.
> 
> DEFINITION (taken from eeh, enhanced by myself)
> 
> |	#include <sys/memsync.h>
> 
> |	void memsync(start, size, what), weakly aliased to
> |	void _memsync(start, size, what)
> 	void* start;
> 	size_t size;
> 	int what;
> 
> where what is:
> 
> 	CACHESYNC
> 
> 	Synchronize data and instruction caches over this region prior to
> |	executing newly generated code in the local execution thread.
> 
> |	CACHESYNC_GLOBAL
> |
> |	as above, but for multi-threaded applications.
> 
> This is identical to CACHESYNC for single CPU machines, or at least
> architectures. However: cgd mentioned (elsewhere) nobody should want this,
> and if yes, that this could be done by STOREBAR (see below),
> application-internal synchronization, and CACHESYNC in all threads. Opinions?
> 
> 	STOREBAR
> 
> |	Force all pending writes to be globally visible (to any device in
> |	the machine, at least if it first executes the equivalent of a 
> |	LOADFLUSH).
> 
> 
> 	LOADFLUSH
> 
> |	Force the next read of that location to pick up global changes
> |	by other devices, at least if they did the equivalent of a STOREBAR
> |	first..
>