Subject: Re: memsync() proposal (Was: Re: cacheflush() proposal)
To: None <email@example.com>
From: Ignatios Souvatzis <firstname.lastname@example.org>
Date: 02/04/1999 22:50:22
I'll start implementation of this soonish.
has the dust settled about CACHESYNC_GLOBAL vs. implementing in
the application using STOREBAR?
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
> 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:
> 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?
> | 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).
> | 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..