Re: TLB tiredown by ASID bump

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Thu, 6 Jan 2011, der Mouse wrote:

> > No.  The existance of ASIDs along with the hardware implementation is
> > fundamentally a proprty of the MMU design.  Exposing this information
> > outside of the MD code base (pmap(9)) breaks encapsulation.
> 
> In detail, yes.  In general, no.
> 
> I haven't looked at the ASID issue in detail.  But it sounds to me as
> though it needs at least a few things elsewhere, though they can (and
> probably should) be kept as general as feasible.  For example, every
> process (or maybe lwp) needs to have an ASID hanging off it - but it
> doesn't have to be done that way; I'd say it should be done by giving
> each process (lwp) a pointer, or maybe a small block of data, which is
> totally private to the pmap in use.  If pmap wants a call at process
> exit, or syscall exit, or whatever, fine - but do it as a
> general-purpose hook which the pmap in use can use to do whatever it
> wants, not just ASID fiddling.

In detail no.  In general no.  I've implemented pmap(9)s that use ASIDs 
and I never needed this feature.  It's all hidden inside pmap(9).  All the 
hooks you should need already exist.

Before adding yet another undocumented general requirement I want to know 
why so I don't get bit in the butt by it when I implent a new pmap(9).  
This just doesn't sound like some weird general external requirement that 
needs to become everyone's headache.

Eduardo