Re: Basic cache questions

[Jun Sun <jsun@mvista.com>]

On Tue, Apr 15, 2003 at 03:19:14PM -0700, Steve Taylor wrote:
> Hello All,   I am hoping some of you mips-linux gurus will be able to help me give me some tips and help me get started on some cache stuff which I want to do. (I know decently well about caches - but only at a theoretical Hennessy & Patterson level - and have just started looking under arch/mips/mm to familiarize myself with the mips-linux implementation).   Here's what I want to do - I have a CPU with 4 way SA I and D caches, and I want to write a module that will lock a certain memory region in these caches (for example, let's say I want to lock the ISR in the I-cache). So my questions are a) Is the kernel going to crash if I try to mess around with the caches like locking out a particular way of the cache or something like that? b) I'm sure there are many issues and complications involved in this that I probably havent even thought of  - any obvious and/or subtle pitfalls? and c) Do you think locking out, say, an entire way of a 4-way cache for a dedicated frequently used !
> !
> routine improves or degrades overall system performance?   TIA, -Steve.

If the cache locking can survive flushing, i.e., locked cache line
remained valid and locked even after cache invalidation ops, I guess
you are probably OK.

I have looked the performance issues with cache locking on a two-way
cache system.  There was not much performance gain.

Jun