What's MMU context?

What's MMU context?

[Wang Yong]

as the source code of linuxPPC, there is a global variable named 
next_mmu_context which is increased by one at each time of create a new
process. what does this mean and what is mmu context? it appears there
is not any mmu context in i386.

Wang


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Re: What's MMU context?

[Dan Malek]

Wang Yong wrote:
> 
> as the source code of linuxPPC, there is a global variable named
> next_mmu_context which is increased by one at each time of create a new
> process. what does this mean and what is mmu context?


I intened to use it on the 8xx processors, as they have an address
space id that allows a TLB optimization so you don't have to
invalidate the entire TLB on context switches.  I assume the
MIPS folks use it as well, since that is where I first used
such an optimization (in an OS other than Linux).  Unfortunately,
the ratio of entries to ASIDs is wrong for my original MIPS-like
algorithm to work, and I never got around to writing something
new.

This was already part of the Linux/PPC port when I started the 8xx
work, and I don't know if other processors use it or if it was
just part of the generic port that was maintained.


	-- Dan

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Re: What's MMU context?

[Wang Yong]

Dan Malek wrote:
> I intened to use it on the 8xx processors, as they have an address
> space id that allows a TLB optimization so you don't have to
> invalidate the entire TLB on context switches.  I assume the

  is this context contained in TLB entry? if yes, do you mean the
entries
  belong to other processes other the current one should not be replaced
  because it contains the integer ID named context?

  the TLB Entry of PPC401D2 contains lower 8 bit of PID. so it doesn't 
  need to flush all entries out when processing task switch. taking this
  into consider, if context of MMU is not useful any more?

  Thank you.
  Wang


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