Subject: Re: memsync() proposal (Was: Re: cacheflush() proposal)
To: None <>
From: Ignatios Souvatzis <>
List: tech-userlevel
Date: 02/07/1999 00:49:03
Another point: we didn't yet define how to do all addresses, 
instead of the given range.
I propose to use the NULL address for this.

$Id: cacheflush.txt,v 1.4 1999/02/06 23:48:02 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

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 start is beginning address of region, 0 == "all of this address space"
|where size is the size of the region
where what is:


	Synchronize data and instruction caches over this region prior to
	executing newly generated code in the local execution thread.


	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?


	Force all pending writes to be globally visible (to any device in
	the machine, at least if it first executes the equivalent of a 


	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