[PATCH] Handle I-TLB Error and Miss separately on 8xx

[Joakim Tjernlund]

> On Jan 19, 2005, at 1:06 PM, Joakim Tjernlund wrote:
> 
> > 8MB pages for user space? Isn't that a bit big?
> 
> Just for kernel space.  I think eliminating lots of TLB updates for the
> kernel will be one of the easiest ways to get a boost of performance
> in this area.  This way, system calls or interrupts won't pollute the 
> TLB
> for the application, which can then just continue to run without having
> to reload the TLB after such events.

I see, similar to the pinned TLBs in 8xx but without the "pin"
This would include vmalloc space and ioremapped space as well?

> 
> Part of my graduate work years ago was MMU overhead with various
> page sizes and replacement algorithms.  Increase page sizes from
> something like 1K to 8M made a difference you could measure, but
> the difference between 1K to 32K made little difference.   Of course,
> you can always write some application that just trashes the TLB and
> proves any improvement incorrect, but that would also trash caches and
> other system resources.  I'll always contend that if you can measure
> the difference between a 4K and 16K page, something else is grossly
> wrong with the system in general and you should be looking for
> performance problems elsewhere.

hmm, did you measure this on a 8xx with that have few TLBs?
I havn't done any measurements, it just seemed like a good idea for
systems with few TLBs and lots of RAM.

 Jocke