About Hardreset on Opteron MB

Eric W. Biederman ebiederman at lnxi.com
Tue Nov 18 19:28:01 CET 2003


Stefan Reinauer <stepan at suse.de> writes:

> * Eric W. Biederman <ebiederman at lnxi.com> [031119 00:16]:
> > So it might make sense to set everything up in a very early pass before
> > memory reset.  Reset the system, and then let the existing resets will
> > not trigger.
> > 
> > Either that or Stefans delayed scheme.   At this point I am not certain
> > which will be easier to maintain.  If we do implement the delayed reset
> > I want to move the memory clear code up into the generic framework so we
> > don't have to clear memory twice.  But if we can get the resets over with
> > before we initialize memory we are in better shape.  That plus something
> > like the kernels quirk interface to handle the various know bits of buggy
> > hardware and we should be ok.
> 
> Would cache-as-ram be an alternative for AMD64 cpus to move the pretty
> complex ht code to a point as early as possible? 

If I can get a commit from a cpu vendor to support it.

> Romcc really does a
> great job, but IIRC the current ht speed code is where it is now because
> it is really hard to do before there is memory.

In part at the time I was just using the 8 general purpose registers.
So we have a little more room.  It is also where it is because that is
a very good general purpose place to put it.  I have found an
instruction that will allow me to extract or insert a bit field into
one of the xmm registers.  Which may also help.

> I also suspect AMD doing a better job in keeping cache as ram
> initialization code the same over different cpu steppings than Intel
> managed with their P-IV.

Well I wrote that code not Intel.  Which was essentially the problem.

It is a support nightmare to have someone plug in a new processor and have
it totally fail because the cache acts differently.  

I have never tried hard on the AMD processors but the limited attempt
I made had problems because of the additional complexity of TOP_MEM
and the io range registers.

I like the idea.  I just rest easier at night with romcc because I
know so new thing won't cause me to rewrite everything.

Eric




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