Subject: Re: VC exceptions

From: Ralf Baechle <[email-masked]>
Date: Mon, 1 May 2000 09:47:50 +0200

On Sun, Apr 30, 2000 at 11:19:41PM +0200, Kevin D. Kissell wrote:

> >Apropriate placement of mappings in the address space isn't always possible.
> >MAP_FIXED is one example.  Aliases in the page cache are harder to handle. 
> >If one of the page cache mappings is writable then readers may even observe 
> >stale data or in worst  case stale data being written to disk.
> 
> mmap() is allowed to fail.  I would think that,  if someone tries to force an 
> unsafe mapping, one should give them EINVAL if one doesn't want to deal 
> with the special case otherwise, or create a copy-on-write clone in a safe
> physical page if one wants to be extra-specially nice...

I'm only worried because I don't know how much software such a change
would break.

IRIX uses something they call page ownership switching.  Essentially they
ensure that only mappings of one colour are accessible at any time.
Accessing a page's mapping of a different colour will make the mm flush
caches, make the old colour inaccessible and the new colour accessible
in the page tables.  That requires a reverse mapping of physical to virtual
addresses, something that Linus so far has always refused to accept.

  Ralf

---

From: [email-masked] (William Fisher)
Date: Mon, 1 May 2000 14:19:50 -0700 (PDT)

> 
> On Sat, Apr 29, 2000 at 06:33:54PM -0400, [email-masked] wrote:
> 
> > What is a r7000?  I've heard of the r8000, is that the same?
> 
> Stupid answer: No, otherwise they'd have the same name :-)
> 
> The R8000 was some kind of CPU hack which SGI came up with when the R4400
> performance was begining to look bad in comparison to the Alphas and the
> R10000 project still would have taken quite some time.  It was featuring
> roughly the integer performance and twice or trice the fp performance of
> a 250MHz R4400 while running at just 75 - 90 MHz.  It was used only by
> SGI.
> 
> The R7000 is kind of a successor to the R5000 featuring roughly R10000
> performance but at a much lower price.  This was developed by either
> IDT or QED mostly for embedded purposes.
> 
	The R5000, was designed and built by QED whom SGI funded to build the processor
	for the O2 product line. SGI still owns the rights via MTI and is allowed to
	license them to the various MIPS Licensees.

	The QED folks ARE the original RXXXX Series designers who originally worked
	for MIPS Computer System until SGI bought the company in 1992. The various
	processor designs which they developed included the R2000/2010, R3000/3010,
	R4000, R4400, R5000 and R7000 processors. Nearly all of the original MIPS
	Computer systems processor designers are now working at QED. MIPS Technoloy
	Inc, MTI, is mostly SGI processor designers and lots of new engineers who
	own the SGI rights to the various MIPS processor designs.

	The R8000 was shipped in a VME based machine which was placed in the
	Challenge line which included R4400, R8000 and R10000 processors. As was noted
	it was an SGI design in total and had a very short life-time.

-- Bill