Re: how i can know the linux-mips implememt cache strategy?

[Ralf Baechle <ralf@linux-mips.org>]

On Wed, Nov 18, 2009 at 10:59:43AM +0800, figo zhang wrote:

> I am porting 24KEC soc to linux new, i have see the mips-kernel impement
> cache strategy: invalid and write-back,
> is it right?  is it implement the write-through strategy? see in
> include/asm-mips/r4kcache.h
> 
> how i can know the kernel using which cache strategy in user space, such
> as how can see the /proc system to know it?

The kernel will always use cache stategy 3 for non-coherent systems and
caching strategy 5 for cache coherent systems.  These two select the most
aggressive caching strategy on all processors and that's what gives the
best performance.

I think write through is just not worth thinking about it.  Early 4K
cores did only implement write through; later models added write-back and
as the result have significantly improved performance.

Minor optimizations of the cacheflush operations for write-through caches
would be possible but I expect only small gains.  R4kcache.h implements a
bunch of helper functions that iterate over memory areas; optimizations
for write-through caches should be done by the callers of these helper
functions.

Again, if you have write-back caches don't even think about write-though.
It almost certainly less effective.

  Ralf