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Re: Does the KA630 have a TB?



Just as an FYI - the first VAX that NetBSD ran on was the 11/750. And I just looked up the specs on that one.

The TB have 512 entries. 256 reserved for system, and 256 for user process.

So the TB can have up to 128K of user process memory cached in the TB.

  Johnny

On 2023-09-24 17:05, Mouse wrote:
I don't think it does, not on any specific size.  I think it, that
version, just depends on its size and replacement policy being such
that that stale entries get replaced before they cause trouble.
[a 300-octet line - TLDR: "depends" may be too strong]

Possibly.  "Depends on" in the sense of "this is the reason it works at
all in view of the missing invalidations".  It _would_ also be accurate
to call it a masked bug; I wrote from the mindset of "why did this even
kinda-sorta-mostly work on a real KA630?".

Given how tiny the KA630's TB is, I suspect it would be quite hard to
find a realistic workload that failed for lack of invalidations,
probably somewhat difficult to construct a synthetic one either using
this kernel (it probably could be done without too much trouble if you
don't care about even attempting to be a UNIXy OS).

It does occur to me that I think I tried, years ago, to run NetBSD on a
more recent VAX - one of the desktop boxes, I think - and failed.  At
the time I probably wrote it off to hardware issues, but I don't
remember the symptom enough, so it could have been this.

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