[rescue] ss2 under load

[Dave McGuire]

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On February 14, Joshua D Boyd wrote:
> >To quote Sun Performance and Tuning (2d edition) by Adrian Cockroft:
> >(page 267)
> > 
> >"A hardware context can be thought of as a tag on each PMEG entry in the MMU
> >that indicates which process that translation is valid for.  The tag allows
> >the MMU to keep track of the mappings for 8, 16 or 64 processes in the MMU,
> >depending on the machine.  Then a context switch occurs, if the new process
> >is already assigned to one of the hardware contexts, then some of its mappings
> >may still be in the MMU and a very fast context switch can take place."
> > 
> >It goes on to say that if you stay under the number of HW contexts, it's
> >actually faster than a TLB system (which is what most things use, including
> >sparcs after the sun4c era).  But if you are on an IPX with 8 contexts and
> >have like 16 active processes, it's got to start purging them out and loading
> >the new active process.  Basically, it's an MMU cache =)
> 
> <snip>
>  
> >Hope this helps.  Granted, if you aren't at all familiar with how
> >virtual memory works, you may just be more confused now... =)
> 
> Thanks.  That clears things up considerably.  So, which machine had the 64
> contexts?

  These are from memory, some may not be accurate:

  pre-mbus machines
  -----------------
  4/100	    8
  4/200	    16
  4/300	    16
  4/400	    64
  SS1	    8
  SS1+	    8
  SS2	    16

  mbus modules
  ------------
  SM100	     4096 (I think)
  SuperSPARC 65536

    -Dave

-- 
Dave McGuire
St. Petersburg, FL         "Less talk.  More synthohol." --Lt. Worf