Re: watch exception only for kseg0 addresses..?

[Daniel Jacobowitz <dan@debian.org>]

On Wed, Dec 04, 2002 at 01:37:13AM +0100, Ralf Baechle wrote:
> On Mon, Nov 25, 2002 at 04:47:33PM +0100, Maciej W. Rozycki wrote:
> 
> > > MIPS64 extends that to also support instruction address matches; the
> > > granularity can be set anywhere from 8 bytes to 4kB; in addition ASID
> > > matching and a global bit can be used for matching.  A MIPS64 CPU can
> > > support anywhere from 0 to 4 such watch registers.
> > 
> >  Actually up to eight -- for all dmfc0/dmtc0 3-bit "sel" values, if I read
> > it correctly.
> 
> Correct but I don't know of any CPU that actually uses more than 4 of the
> possible 8 sets atm.  So we're both right :)
> 
> > > The global bit stuff would only be useful for in-kernel use, I think.  The
> > > ASID thing could be used to implement watchpoints for an entire process, not
> > > just per thread though I doubt there is much use for something like that.
> > 
> >  Well, there are two options only -- either use global matching or ASID
> > matching.  What else would you expect?  Do you mean lazy vs immediate
> > switching? 
> 
> Basically there would be two possibilities, associate the debugging state
> of a process with it's thread_struct or with it's mm_struct.  The latter
> would have a little less impact on the context switching performance,
> the first be a bit more flexible.

Thread_struct, please.  Just because two processes have the same
mm_struct doesn't mean that we want watchpoints to trigger in both of
them, unless specifically requested.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer